Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~ 1~3~197
1 T-2643-Z89
LE~ACID B~TE~ AND MEE~D OF M~KING ~E
The present invention relates to storage
batteries, and, more particularly, to lead-acid storage
batteries characterized by a high cranking power to
weight and volume ratio.
The last several years have seen a number of
developments in the lead-acid battery field for
starting, lighting and ignition (hereinafter "SLI")
applications, perhaps the most significant of which is
the maintenance-free battery. Ideally, this type of
battery allows use over its service life without the
need for any maintenance, such as adding water or the
like. The popularity of the maintenance-free battery
for SLI applications is widespread at the present
time.
However, the battery industry is continually being
faced with seemingly ever-increasing demands. There is
thus considerable pressure on automobile manufacturers
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~ 173~9~
to provide improved performance, e.g. - better gas
mileage; and this translates to ef~orts to reduce the
overall weight of the automobile as much as possible.
Lighterweight batteries are like~wise being required so
as to contribute to weight reductions. Similarly, there
is a tendency for requiring a smaller-sized battery,
simply due to the amount of space available under the
auto bile hood.
At the same time, the number of smaller-sized
automobiles with smaller engines currently in service
has risen dramatically. While the batteries used for
such smaller automobiles can be smaller, the designs
required need to be more efficient. Thus, for example,
reducing a 350 cubic inch engine to one one half that
size does not allow reducing the battery performance
requirements to the same extent. The starting or
cranking power, as one example, which is required for
such a smaller engine, is thus more than one-half of
the requirement for the 350 cubic inch engine.
Moreover, four cylinder engines require substantially
higher cranking speed to attain engine starting.
Indeed, some four cylinder engines require up to one
and one-half to three times the cranking speeds of V-~
engines.
The increase in popularity of diesel-powered
automobiles has also contributed to the demand for more
efficient batteries. Engines of this type ~hus require
more starting power than a comparably sized
gasoline-powered engine. As a result, it is not
unusual to see a diesel-powered automobile employ two
batteries in parallel or utilize an extremely large
battery, almost approaching a truck battery size.
3 ~ ~3~19~
These and other considerations dictate that
battery manufacturers provide a battery with
substantially improved performance characteristics.
This need has engendered considerable attention.
Substantial effort has thus been directed to
enhancing performance of present battery designs by
attempts to improve individual components. One example
of this are various efforts to provide improved
performance by modifying the grid design. U.S. Patents
4,118,553, 4,221,852 and 4,221,854 are specific
examples. While perhaps providing some improvement,
batteries incorporating such grid designs fall far
short of satisfying the ever~increasing requirements
being faced by battery manufacturers.
Another attempt to reduce the weight of a battery
comprises the use of a plurality of frames, each
divided into a number of side-by-side positive and
negative active paste support areas. These frames are
assembled and secured together in a stack configuration
so that the perimeter portions of the frames serve as
the top, bottom and two opposite sides of the battery;
and the divisions in the frames serve as cell
partitions. Each frame is pasted with active material
to provide plates, with adjacent plates in each frame
being of opposite polarity, and adjacent plates in
adjoining frames also being of opposite polarity. This
type of battery construction is exemplified in U.S.
Patent 4,022,951 to McDowall.
Such a battery construction is said to reduce the
battery weight and size considerably as well as to
eliminate the formation of intercell connections during
assembly, with the avoidance of sealing problems, as
well as the possible elimination of the requirement for
a separate battery case.
3 ~ 7
However, this type ~f battery construction is not
amenable to conventional battery assembly techniques.
Utilization would thus require new and different
assembly equipment~ creating both a considerable
capital investment as well as ~he necessity of gaining
knowledge as to what is required from the quality
control standpoint. Moreover, it would be difficult,
if not impossible, to make the combination positive and
negative grids from different alloy materials. As is
known, the use of hybrid grids for maintenance-free
batteries is often desirable, or even necessary, in
some applications. Still further, joined positive and
negative grid type of construction would make it qui~e
difficult to automate the pasting of active material
precursors onto the grids while using separate paste
formulations for the positive and negative plates, as
is generally practiced. It would also seem difficult
to maintain satisfactory electrolyte-tight sealing
throughout the service life because of the considerable
area of the frames which must be heat-sealed together
and the number and type of cell-to-cell connections
which are necessary. Thus, in this type of
construction, the area which must be heat-sealed could
well be about 25 to 50 times that required in the
~5 cover-to-container seal in a conventional battery
design. No battery manufacturer has yet been able to
demonstrate the reliability that would be required to
carry out a heat-sealing operation of this magnitude on
a commercial scale.
The McDowall type of combination positive-negative
plate construction is representative of the approach
wherein cell-to-cell connection is obtained by the
combination plate support member in one cell extending
1 1 ~ 3 ~
through the partition and serving as the support member
of the plate of opposite polarity in an adjoining cell.
All of such approaches would require relatively complex
assembly techniques when considering commercial
production.
Still further, prior patents and literature in the
battery field are replete with a multitude of
configurations and theories for providing improved
battery performance by reducing the internal
resistance. Yett despite all this substantial prior
effort, there still remains the need for a relatively
lightweight, small volume battery which can be reliably
made on a commercial production basis while providing
the ever-increasing performance characteristics being
demanded. Stated another way, there still exists a
need for a battery which can reliably be made on a high
volume, production basis which is characterized by a
high cranking power to weight and volume ratio , e.g. -
starting power for an automobile, while maintaining the
other characteristics required to provide an SLI
battery with a satisfactory useful service life.
A principal object of the present invention is
thus to provide a storage battery possessing superior
power per unit weight and volume characteristics.
A further object lies in the!provision of a
battery amenable to high volume, commercial scale
production.
Yet another object of this invention provides a
battery which utilizes many of the conventionally used
battery assembly techniques. A related and more
specific object provides a battery which can utilize
battery containers of conventional design and
standardized external dimensions. A further and
3 '1 ~ ~
related object provides a lead-acid battery capable of
using conventional pasting techniques and separator
materials.
Another object of the present invention is to
provide a storage battery having a reliable
electrolyte-tight sealing structure.
Yet another object of this invention is to provide
a battery in which the elements of a cell can be
inserted into the battery container as a unit.
Yet another object provides a storage battery
which can utilize a hybrid grid alloy construction
which allows selecting the grid alloy to achieve
optimum positive and negative plate performance.
Other objects and advantages will be apparent from
the accompanying drawings, in which:
FIGURE 1 is a perspective view of the battery of
the present invention with one end wall being partially
cut away to show the connection in the end cell to one
terminal and the intercell connections;
FIG ~ 2 is a side elevation of the battery of the
present invention and partially cut away to further
illustrate the intercell connections;
FIG. 3 is a top plan view of the battery of this
invention and partially cut away to show the
positioning of the separator, element straps and
intercell connections;
FIGr 4 is a cross-sectional view taken generally
along line 4-4 of FIG. 3 to illustrate further
constructional features;
FIG. 5 is a schematic view of a grid suitable for
us~ in making the plates; and
FIG. 6 is a schematic view of a grid suitable for
making an alternative embodiment.
9 ~
While the invention will be described in
connection with preferred embodiments, it will be
understood that we do not intend to limit the invention
to these preferred embodiments. On the contrary, we
5 intend to cover all alternatives, modifications, and
equivalents as may be included within the spirit and
scope of the present invention as defined in the
appended claims. Thus, while the present invention
will be described in conjunction wi~h a SLI automotive
battery, it should be appreciated that the invention is
equally applicable to any other lead-acid battery
application. Indeed, the present invention can be
adapted to use with an absorbed electrolyte type of
battery, as opposed to the flooded-electrolyte battery
illustrated herein. Use of the present invention will
be particularly advantageous in applications which
require relatively high peak power per unit weight or
volume.
In general, the present invention is predicated on
the discovery that, by a unique combination of physical
parameters, as will be discussed hereinafter, a lead-
acid battery can be provided which is characterized by
exceptionally high power characteristics per unit
weight or volume. Such characteristics are highly
advantageous in applications such as automobile
starting.
This improvement in performance can be
quantitatively set forth in terms of peak power per
unit weight of the battery, or per unit volume, of the
battery. Peak power is defined in the Society of
Automotive Engineers (SAE) publication No. 660029,
January 10-14, 196~, titled "Battery Ratings" by Kruger
and Barrick. This parameter provides a means for
.~. 173L1~
determining the maximum cranking power that a battery
will provide for startin~ an automobile. The perform-
ance of batteries in accordance with the present
invention are characterized in an optimized configura-
tion by a peak power, measured at 0F., of at leastabout 200 watts~pound of the gross weight of the
battery and at least about 15 watts/cubic inch based
upon the total volume ~i.e.- nominal external volume
discounting terminals) of the battery, preferably at
least about 225 to 235 watts/pound or more and about 17
to 20 watts/cubic inch. Based upon the effective
volume of the battery (i.e.- the internal volume minus
the head space above the electrolyte level), batteries
in accordance with the present invention are capable of
providing peak power of at least about 30 watts per
cubic inch or so.
The lead-acid batteries of the present invention
are also characterized by extremely low resistance-
weight equivalents, viz.- a value representing the
product of the average internal resistance of a cell of
the battery multiplied by the total weight of the cell.
This value is determined by dividing the total internal
resistance of the battery by the number of cells and
multiplying this resulting number by the total weight
~5 of the battery divided by the number of cells. Measured
at 0F., batteries in accordance with the present
invention in an optimized configuration provide
resistance-weight equivalents of about 4.6 milliohm-
pounds or less, preferably less than about 4.1 and,
more preferably less than about 3.9.
By an "optimized configuration'i in the discussion
herein, it is meant that the cell element occupies
substan ially the entire internal cell ~olume in the
'~ ~7'3~197
battery container, as will be more ~ully described
hereinafter. However, the present invention can
utilize, if desired, an over sized container relative
to the size of the cell element required for the
particular performance characteristics. This may be
desirable, for example, in the battery replacement
market where particular applications require
standardized battery container sizes.
In these instances, the advantages of the present
invention are derived principally from cost savings,
as, for example, resulting from more efficient lead
utilization. Such advantages can be seen by reference
to the resistance lead weight equivalent. This
parameter is a measure of the effective utilization of
the lead in the battery and is most usefully
characterized on a per cell basis to provide an average
value. This is determined by dividing the total weight
of lead in the battery (viz. - the total weight of the
lead component, in free and in combined form, in all of
the components of the battery; stated another way, the
total weight of metallic lead and lead compounds
present in the battery as determined on a dry, unformed
basis) by the number of cells and then multiplying that
figure by the value determined by dividing the total
internal resistance of the battery by the number of
cells. Measured at 0F., the batteries of the present
invention are characterized by resistance-lead weight
equivalents of no more than about 3.3 milliohm-pounds,
preferably no more than about 3~0, more preferably no
more than about 2.85, and even more preferably less
than about 2.7 or 2.5. The corresponding peak power
level based upon the weight of the lead in the battery
3~
is at l~ast about 280 watts per pound lead, more
preferably at least about 340 watts per pound lead.
The batteries of the present invention may also be
characterized in relation to the O~F. Cold Performance
test which is standard for the United States automotive
battery industry. In this test, a battery is rated at
the number of amps (termed "cold cranking amps") which
can be drawn from the battery while providing a voltage
at 30 seconds of no less than 7.2 volts. This Cold
Performance test is considered to provide a measure of
the starting power of the battery. Batteries of the
present invention in an optimized configuration are
characterized by cold cranking currents of at least
about 1~ amps/pound based upon the gross weight of the
battery, preferably at least about 17.5 amps/pound, and
more preferably, at least about 20.0 amps per pound.
Considered by volume, batteries in accordance with this
invention typically provide at least about 1.5 cold
cranking amps per cubic inch based upon the total
volume, more preferably at least about 1.7 amps per
cubic inch. Based upon the effective volume, batteries
of the present invention provide at least about 202
cold cranking amps per cubic inch, more preferably at
least about 2.5 cold cranking amps per cubic inch.
Based upon the total weigh~ of lead in the battery,
batteries of the present invention provide at least
about 30 to 31 cold cranking amps/pound of lead
weight.
To provide a specific example of what these
parameters mean, a commercially available, Group 24
maintenance-free, 12-volt battery, nominally rated at
550 cold cranking amps, weighs about 42 pounds and
employs a container having a total volume of about 577
3'~
11
cubic inches. In marked contrast, a battery made
according to the present invention and also nominally
rated at 550 cold cranking amps, will weigh about 30
pounds or so and can be placed in a container having a
total volume of only about 345 cubic inches. On the
other hand, a battery utilizing the present invention
with a container volume of the same external dimensions
as the commercial battery described above will provide
a nominal cold cranking rating of about 850 to 900 amps
or so, the weight of such battery being about 3 to 4
pounds heavier than the above Group 2~ commercial
battery.
This marked difference in performance may also be
seen by comparing the peak power characteristics. The
Group 24 commercially available battery provides a peak
power of about 5120 watts at 0DF. which translates to
about 121 watts per pound of the battery and about 8.9
watts per cubic inch based upon the total volume. The
battery of the present invention, by way of contrast,
provides a peak power o~ about 7000 watts, corre-
sponding to about 230 watts per pound and about 20.3
watts per cubic inch, based upon the total volume.
These exceptional battery performance
characteristics permit the battery of the present
invention to provide starting or cold cranking power
which is equivalent to some truck batteries that weigh
substantially more. In some cases, batteries according
to the present invention, weighing 35 pounds or so,
have provided more cranking power than some truck
batteries weighing over 100 pounds.
Turning now to a more detailed description of the
present invention, there is shown in FIGS. 1-5 a
preferred embodi~ent of a 12-volt, 6-cell battery of
~. ~73~97
12
the present invention. As seen in FIG. 1, the battery
10 comprises, in general, a premolded container 12, a
cover 14 attached to the container by any suitable
means, a positive terminal post 16 and a negative
terminal post 18. While illustrated as top terminals,
side terminals or other terminal configurations could
likewise be employed.
The container 12, as best seen in FIGS. 2-4, is
divided into a plurality of cells by integrally formed
partition walls 20 which lie in generally equally
spaced planes essentially parallel to the end walls 22
of the container 12.
Each cell has a plurality of independent,
alternately disposed, positive electrode plates 24 and
negative electrode plates 26. As illustrated, in
accordance with one preferred aspect of the present
invention, the plates 24 and 26 are disposed generally
perpendicularly to the cell partitions 20.
When positioned in this fashion in conventionally
sized automotive battery containers, i.e., - batteries
having standardized external dimensions for example, as
set by S~E for automotive batteries in the United
States and by other organizations in other countries,
such as Deutsche Industrielle Norme (DIN) of the
Federal Republic of Germany, the height to width ratio
of the plates will be at least about 2:1, often at
least 3:1 or more, perhaps up to about 4:1 or 5:1.
In accordance with the present invention, the
total area of the plates is about one-fourth to one-
sixth that of the area of conventionally sized SLIplates. This corresponds to a plate area for an
individual plate of about 5 to about lO square inches.
It has been found that plates within this area range
13~19~
13
.
are satisfactory to provide the desired power charac-
teristics for batteries in accordance with the present
invention. It is believed that such relatively small
plates provide a more e~fective utilization of the
conductive portions of the plates, as will be more
fully discussed hereinafter~
FIG. 5 sets forth an illustrative example of a
useful independent supporting and electrically
conducting member, viz.- grid, for the electrode
plates 2~ and 26. The grid, shown generally at 28,
includes an outer frama bar 30, cross wires 32 and 34
which intersect to ~orm generally equivalent windows or
active material pellet areas 36, an electrical
connection means such as a plate lug 38 and a foot 40.
The grid design shown is only exemplary, and many
other configurations could be used as the particular
design is not critical. All that is required is that
the grid adequately function to support the active
material which must be included to make up the
electrode plate and to relatively efficiently carry the
current generated to the collection point, viz. - the
plate lug 38. As may be appreciated, however, the use
of more efficient grid designs could contribute to
further reductions in internal resistance and,
consequently, improved electrical performance.
In accordance with one aspect of this invention,
the grids utilized are relatively thin. It has thus
been found suitable to utilize grids having a nominal
thickness in the range of about 0.030 to about 0.065
inch, more preferably about 0.035 to about 0.045 inch.
The nominal thickness will typically be determined by
the thickness of the outer frame bar 30, as the cross
wires 32 and 34 are generally somewhat thinner than the
1 ~73~l~7
14
frame ~ar 30. ~rids thicker than those described
herein may be employed but may detract somewhat from
the performance obtained. On the other hand, grids
thinner than about 0.030 inch can conceptually be used.
However, the manufacture of extremely thin grids is
quite difficult with existing technology. Moreover,
the service life requirements needed should be taken
into consideration as the corrosion which will occur in
service may dictate the minimum thickness which is
desirable. It is generally desired to maintain the
weight of the grid at about 1.5 to about 2.0 grams per
square inch of grid area. The weight per unit area
employed will typically increase as the area of an
individual plate is increased.
The alloy used for the grids is not particularly
critical~ Many suitable alloys for lead-acid battery
grids are known. However, in view of the widespread
usage of maintenance-free batteries, it is preferred to
utilize alloys capable of achieving maintenance--free
performance. Many alloys of this type are likewise
known and may suitably be employed. Where maintenance-
free applications require optimum cycle life, it is
preferred to use a low antimony, maintenance-free alloy
for the positive grids and an antimony-free alloy for
!' 25 the negative grids.
The grids may be made by any suitable tecnniques.
Techniques using casting or expanded metal are known
and may be utilized.
To provide the electrode plates, appropriate
positive and negative active material or its precursor
must be applied to the grid which serves as a support
for such material. This can be accomplished by using a
conventional active material (or a precursor) formula-
tion and then applying such formulation to the grid, as
1~3~97
by pasting or otherwise applying such formulation onto
the gridr as is well known.
The use of independent positive and negative
electrode plates allows maximum flexibility in design.
Different alloys and different active material (or
their precursors) formulations may thus be employed;
tailored to give the optimum performance for the
particular intended batte~y application.
From the functional standpoint, only that amount
of paste weight per unit area is utilized which is
necessary to satisfy the desired cold cranking perform-
ance. Excessive amounts will tend to detract from
power per unit weight or volume efficiencies; however,
other performance requirements (e,g.- reserve capacity)
may dictate the use of greater amounts of paste. At
conventionally used densities, it has been found
suitable to employ dry pasted weights on the order of
about 2.5 grams per square inch of plate area when a
grid thickness of about 0.040 to 0.045 inch is used.
As is conventional, separator means are used to
separate the positive and negative electrode plates.
Any separator means useful for lead-acid batteries may
be employed. It has been found suitable to space the
electrode plates in the battery of the present
invention with the same spacing as used in conventional
lead-acid batteries, viz. - typically about 37 mils
(0.037 inch) apart. The separator means used should
desirably include ribs or other means to allow gas
generated at the electrode plates to escape upwardly
out of the container 12.
In accordance with yet another and pre~erred
aspect of this invention, the separator means in each
cell comprises a continuous strip of separator material
73~(3~
16
which is fol~ed in accordion fashion, with the positive
and negative electrode plates being alternately
positioned in folds on opposite sides of the separator
material. To this end, the separator 42 in each cell
illustrated in FIGs. 1-4 is a continuous strip of
material folded in accordion fashion~ Materials useful
for maintenance-free applications are preferred. For
such applications, it has thus been found satisfactory
to utilize commercially available silica-polyethylene
separator materials. As one specific example,
materials of this type in a nominal 10 mil thickness
with ribs to provide electrode plate spacings of about
37 mils have been found satisfactory. The ribs should
face the positive electrode plates and be configured to
provide a path to allow the gas generated to escape
upwardly and ultimately out of the container. One
method of assembly of the separator and plates into a
cell element stack is described in the co-pending
Oswald et al application described herein. The
particular assembly method used does not form a part of
the present invention.
The separator resistance and the spacing between
electrode plates will affect the overall internal
resistance of the battery. To provide optimum
performance, it is accordingly preferred to utilize a
separator having a resistance, at 80F., of no more
than about 10 milliohm-in.2 (~ 2 milliohm-in.2) or
so; and the commercially available silica-polyethylene
materials described herein meet this criteria.
Separators with higher resistances can, of course, be
utilized, depending upon the electrochemical perform-
ance characteristics desired for the particular battery
application.
.
3 ~-1 9 ~
Similarly, providiny closer plate spacing than 37
mils will decrease the internal resistance due to the
electrolyte. Increasing the spacing will have the
opposite effect.
The performance characterisl:ics of the batteries
of the present invention described herein have been
derived using a 37 mil electrode plate spacing with a
separator meeting the preferred resistance criteria
described. ~s should be apparent:, some or all of the
advantages of this invention can be derived by
utilizing less than an optimum combination of plate
spacing and separator resistance. Thus, many
separators with resistances in the range from about 12
to 30 milliohm-in.2 are available and are often
employed in lead-acid battery applications. Use of
such higher resistance separators will detract somewhat
from performance but may be acceptable for some appli-
cations. For example, use of a separator with a
resistance of about 30 milliohm-in.2 and 37 mil
spacing will provide a battery in accordance with this
invention having a resistance-weight equivalent of
about 4.9 milliohm-pounds.
Suitable venting means for the battery may be
provided, as is conventional; and any of the several
conventional vent plugs may be used. As best seen in
FIGS. 1 and 2, the illustrative embodiment provides a
single vent for each cell, the vent plug, shown
generally at 44, being of the type often used for
commercially available maintenance-free automotive
batteries. Internal gasses escape through channels
formed on the underside of cover inserts 46 which are
press fitted into the cover 14.
18 ~ 173~19~
Means should also be provided to minimize the
possibility of internal shorts occuring due to sediment
collecting in the bottom of the container. More
particularly, as is known, battery use results in
shedding of active material and the like which then
collects in the bottom of the container. This
sediment buildup can create an e:Lectrical path which
bridges adjacent positive and negative electrode
plates, thereby creating an internal short.
Such means can be provided by molding the bottom
of the container 12 with upstanding ribs or shoulders
48 adjacent and generally parallel to the partition
walls of the cells, as is best seen in FIG. 2. These
ribs or shoulders 48 cooperate with the feet 40 of the
electrode plates to position the plates sufficiently
above the cell bottom so that, in service, any
conductive bridges that would otherwise result in
internal shorts being created should be avoided. The
particular distance that the lower part or bottom of
the electrode plates are maintained above the bottom of
the cell can be similar to that used in conventional
battery construction.
More preferbly, and as is employed in some
commercial maintenance-free batteries, the bottom of
the cell can be filled with an electrolyte-resistant
adhesive, such as an epoxy resin, sealing compound, or
hot melt, sometimes used in the battery industry, so
that the electrode plates and/or separators are potted
in place. Securing the bottom of the plates, or the
foot 40 of the plates in the illustrative embodimentr
will provide improved vibration resistance.
Still further, and as will be described in more
detail hereinafter, the electrode plates and separators
~ 3L73~1~7
19
can be suspended in the cell by the intercell connec-
tion means used so that there i5 adequate spacing from
the cell bottom. In this instance, it will generally
be desirable to size the separator so that its lower or
bottom edge slightly overhàngs the bottom of the
electrode plates, as is shown in FIG. 2.
For optimum performance characteristics, as has
been previously noted, it will generally be desirable
to size the element stack employed so that the cell
element stack, formed by the electrode plates and
separator, will snugly fit in the container cells. In
other words, the cell element is sized relative to the
cell so that it can just be conveniently inserted. The
tolerance between the cell element and the cell side
walls may thus suitably be about 1/16 or 1/32 of an
inch to provide a snug fit. This sizing allows optimum
usage of the available internal battery space, and, in
this respect, an optimized configuration~
Alternatively, and as is illustrated in FIG. 3,
ribs shown at 50 may be integrally molded into the
sidewalls 52 of the plastic container 12 to hold the
cell element in position when an oversized container is
used. Indeed, if desired, an oversized container can
be employed without the need for ribs or other
positioning means. However, in such instances,
electrolyte, in excess of that needed for satisfactory
operation, will be present so that the use of a
suitable lightweight foam or other volume-reducin~
means may be desirably employed to displace such excess
electrolyte, thereby providing a lighterweight
construction.
In accordance with this invention, conductive
element straps electrically connect in parallel plates
20 ~-~73~lg'~
of like polarity in each cell element. The electrical
connections may be carried out by any of the
conventionally used techniqueS, typically providing a
fused connection.
Thus, in one end cell, as is illustrated, a first
conductive strap is electrically connected to the
electrical connection means or lugs of each of the
independent positive electrode plates and to the
positive terminal. As shown, in FI~s. 1 and 2, a
strap 54 i~ accordingly connected to the lugs 38 of the
positive electrode plates 24 and, in turn, to the
positive terminal 16.
In the other end cell, a second conductive strap
is electrically connected to the electrical connection
means or lugs of each of the independent negative
electrode plates and to the negative terminal. Strap
56, as seen in FIG. A, is thus connected to the lugs 38
of the negative electrode plates 26 and, in turn, to
negative terminal 18.
Similarly, a third conductive strap61 connects in
parallel to each of the ~ e~ent positive electrode
plates in each cell other than the positive terminal
cell. Likewise, a fourth conductive strap in each cell
other than the negative terminal cell electrically
connects in parallel each of the negative electrode
plates~ A fourth conductive strap 60 in each cell
other ~han the negative terminal cell is thus
electrically connected to the lugs 38 of each of the
negative electrode plates 26.
1 1'~349'`~
21
Pursuant to yet another aspect of the present
invention, at least two intercell connectors per cell
electrically connect in series adjoining cells. In the
preferred embodiment, the intercell connectors use a
through-the-partition configuration. The number of
intercell connectors utilized wi:Ll in large part be
determined by the number of plates per cell. Many
applications make the use of at :Least three intercell
connectors preferable. In some applications where an
extremely large number of plates per cell are used,
e.g. - about 60 or more per cellv it may be desirable
to utilize four intercell connectors to connect
adjoinin~ cells. To this end, and as illustrated in
FIGs. 1-4, the third conductive strap 61 has three
upstanding intercell connector buttons 62 which a~ut
apertures 64 in the cell partitions 20. The fourth
conductive strap 60 in the adjoining cell has three
upstanding intercell connector buttons 66 which
likewise abut apertures 64. In the assembled condition
illustrated, buttons 62 and 66 are shown fused
together, resulting in electrolyte-tight, intercell
connections.
The intercell connections are suficiently strong
so that, if desired, the positive and negative
electrode plates can be suspended from the conductive
straps without additional support at the bottom of the
plates being required. This may be particularly useful
where the grids forming the supporting member for the
electrode plates are made by expanded metal techniques.
It is believed that these multiple intercell connec-
tions provide a battery which is less prone to damage
caused by vibration, as could result from use in
service or the like.
, ~ ~ 3 '~ ~ ~
The respective conductive straps, as well as the
intercell connector buttons associated with the ~hird
and fourth conductive straps, can be connected to the
respective positive and negative electrode plates
either before or after insertion into the battery
container. It is preferred to utili~e an element stack
as described in the related application identified
herein, inasmuch as the m~ltiple components required
can be then easily handled as a unit. This element
stack can be subjected to a cast-on-strap operation by
which the straps and buttons can be cast on the lugs in
a single operation to provide a cell element. Conven-
tional cast-on-strap techniques are known and may
suitably be utilized. After the cell elements are in
position in the container, the intercell connections
can be made by electrical welding or gas-burning
techniques to form the fused intercell connections
shown in the illustrative embodiment.
The formation of the active material precursor
paste typically used can be carried out by known
techniques. Thus, formation may be carried out in a
one step operation using a sulfuric acid electrolyte
with a relatively high specific gravity, e.g.- 1.200 or
so, or in a two step procedure involving charging in a
relatively low specific gravity electrolyte, e.g.-
1.060 or so, followed by dumping and then soaking with
a higher specific gravity electrolyte. In either
event, the full charge specific gravity of the
electrolyte for SLI service applications will be in the
range of about 1.265 or so.
The level of electrolyte in the container can be
varied as desired but will generally be up to the top
~ ~73/197
23
of the electrode plates. This is all that is required
to provide the electrical performance characteristics
of the batteries of this invention. However, in
flooded-type batteries, it is useful to provide a level
above the electrode plates so that a reservoir, in
effect, of excess electrolyte is created, both for
maintenance-free applications as well as for improved
lower rate performance (e.g.- reserve capacity).
As can be seen, the illustrative embodiment
provides efficient intercell connection. The conduc-
tive straps electrically connecting plates of like
polarity within the inter-connected cells are thus
adjacent, generally parallel to, and extending
substantially the length of the cell partition in an
optimized configuration. This efficient intercell
connection contributes to the vastly superior cranking
power performance characteristics exhibited by the
batteries of this invention.
To provide the lead-acid batteries of the present
2~ invention, the several physical parameters discussed
herein are selected relative to each other to provide
the exceptional power per unit weight or volume
characteristic of such batteries. It is the inter-
relationship of such parameters which achieves such
characteristics.
The relatively small area of an individual plate
in comparisGn to conventional SLI lead-acid batteries
contributes substantially. This provides an extremely
efficient conductive member. At a given total plate
area, the use of more plates, each of drastically
reduced area, dramatically reduces the internal
resistance of the battery.
~ ~3~
2~
This high efficiency allows the weight or mass of
the grid portions of the plates per unit area to be
substantially reduced. The reduction in mass affects
the balance between the resistance due to the
electrolyte and the electronic resistance due to the
plate. The mass of the grid selected should be such as
to provide a relatively optimum balance, the balance
being quite different from the balance used in conven- -
tionally designed batteries. Stated another way, the
mass will desirably be selected such that either
increasing or decreasing the grid weight per unit area
will not increase to any significant extent the power
characteristics per unit weight. This reduction in
mass may correspond, as an example, to about 91 percent
per unit area of that used in conventional batteries.
Further, using typical automotive paste densities,
the mass per unit area of the active material paste
employed is reduced significantly. Thus, the active
material paste mass per unit area is reduced to only
~0 that amount necessary to satisfy the desired cranking
requirements. As an example, the total paste mass per
- unit area may be about 83 percent of that convention-
ally used.
Accordingly, the total plate mass per unit area of
batteries in accordance with the present invention is
about 86 percent of that of conventional batteries.
As is known, the cold cranking performance of
lead-acid batteries is, in general, dependent upon the
effective total plate area. Thus, to actually deliver
a particular cold crank rating, a minimum effective
total plate area is needed. If that minimum is not
provided, the average current density (based upon the
effective plate area) which results will change the
~ 1~3'1~7
slope of the voltage-time curve to the extent tha~ the
battery may well fail the cold performance test. As an
example, conventional batteries are generally designed
such that the average current Aensity does not exceed a
value in the range of about 1.8 amps per in.2 or so.
In contrast, the batteries of the present
invention are characterized by relatively high terminal
voltages (e.g.- 5 second voltage). This allows a
reduction in the effective plate area neede~ to deliver
a particular cold crank rating since the sharper slope
of the voltage-time curve that will result should still
provide the required 7.2 volts after 30 seconds. Thus,
as an example, a battery pursuant to the present inven-
tion may be designed such that the average current
density is in the range of about l.9 to 2.2 amps per
in.2. This allows the effective plate area in the
batteries of this invention to correspond to about 88
percent of that needed in conventional batteries.
Still further, a plate surface which does not face
the surface of a plate of the opposite polarity does
not contribute to any significant extent to the
effective plate area, as there is an extremely high
resistance path to any plate surface of opposite
polarity. On each side of a cell, the outer surface of
the two outside plates is thus substantially wasted.
As one example, the percentage of wasted plate area in
a conYentional battery may be on the order of 9 to 10
percent. In batteries pursuant to the invention, the
wasted plate area, as an example, can be reduced to
about 1.8 to 2 percent or so. Due to this end plate
effect, the total plate area of the batteries of this
invention need only be about 92.5 percent of that in
conventional batteries.
:~ 1'73~.97
26
While the magnitude o any one of these three
weight and area reduction effects is significant, the
cumulative effect is dramatic. The total lead weight
of the plates required to provide a battery pursuant to
the present invention with power characteristics (e.g.-
cold cranking performance) equivalent to that of
conventional batteries is only about 70 percent or so
(viz.- .86 x .88 x .925 x 100) of that required in
conventional batteries.
It should also be appreciated that the efficient
intercell connection previously clescribed likewise
contributes significantly to the improved performance
of the batteries of this invention. Thus, the total
top lead (viz.- weight of straps and terminals) may be
reduced to abo~t 75 percent of that used in conven-
tional batteries due to the efficient current paths of
the intercell connections of batteries designed in
accordance with this invention. It has also been found
that the internal resistance of the intercell connec-
tions of such batteries is about 75 percent of that ofconventional batteries. The net effect is that the
cell-to-cell connections of the batteries of this
invention may be on the order of about twice as
efficient on a unit lead basis as that of conventional
25 batteries. !'
Still further, since the lead weight of the plates
per unit area has been reduced, the amount of electro-
lyte may likewise be correspondingly reduced. This
also contributes to the improved power characteristics
per unit weight of the batteries of this invention.
'
.~L 1 71 3 ~ 9 ~
This unique interrelationship of physical
parameters together with the efficient cell-to-cell
electrical connections provide a battery characterized
by, at a nominal rated cold cranking, an extremely high
initial terminal voltage ~e.g.- 5 second voltage),
viz.- on the order of, typically, 8.3 to 8.6 volts or
so in relation to that of conventional batteries which
vary from perhaps about 7.4 to 7.9 volts or so. What
this means from a production standpoint is that
internal resistance as a cause of failure upon cold
cranking is virtually eliminated. This is in marked
contrast to conventional batteries where the margin of
error (i.e.- the increment of the initial terminal
voltage above 7.2 volts) may be so small that, through
manufacturing variation or the like, the battery will
not deliver its rated cold crank. Moreover, even when
compared with conventional batteries of identical cold
crank rating, batteries pursuant to the present
invention possess significantly higher power which
translates to substantially greater starter and, thus,
engine cranking speed for starting an automobile.
The foregoing subsumes the desire to optimize the
power characteristics per unit weiyht or volume.
Particular applications may make it desirable to
provide greater low rate capacities, e.g.- reserve
capacity, which may detract somewhat from such power
characteristics. For example, to provide more reserve
capacity, it may be useful to increase the mass of
active paste over that discussed above. This will
diminish somewhat the power characteristics; yet, such
characteristics will still remain substantially
superior to that of conventional batteries.
3 '`I ~
28
Conventional battery designs can be modified to
gain some of the advantages of the power characteris-
tics of this invention. To this end, by providing
electrode plates of conventional size with at least two
connector lugs and with at least two through-the-
partition connections, and preferably at least three,
performance is significantly enhanced. Thus, in a
conventional 13-electrode plate cell element, a total
of at least 39 lugs per cell will be utilized in the
preferred embodiment. A suitable grid 68 for
accomplishing this alternative embodiment is shown in
FIG. 6. The grid 68 includes an outer frame bar 70,
cross wires 72 and 74, and multiple lugs 76, 78 and 80.
The lugs for the positive and negative grids should, of
course, be offset so that the necessary conductive
straps and intercell connections can be made. In any
event, the particular electrode plate configuration
employed should provide at least one lug per about
every 14 square inches of electrode plate area, more
preferably, at least one lug for every 12 square
inches.
In addition, modifying the physical parameters of
a battery utilizing the multiple lug plates in
accordance with the principles discussed herein should
further enhance the power characteristics when compared
to those of a conventional battery. The resulting
battery should thus possess power characteristics on
the order of those described for the preferred embodi-
ment of this invention. It is not, however, believed
that this alternative embodiment can equal the more
preferred power characteristics of the preferred
embodiment.
~ 1~3'~9~
29
Also, this alternative design may make the
connection to the terminals quite cumbersome. It may
therefore be desirable to modify the con~truction of
the plates of one polarity in its terminal cell by
utilizing a single lug per plate, and, thus, a single
strap, positioned adjacent the terminal. This will
detract from the desired power characteristics but may
be preferable to the manufacturing problems likely
associated with a construction requiring multiple,
spaced straps to be connected to the terminal.
The following Examples are illustrative of, but
not in limitation of, the present invention.
EXAMPLE 1
A series of batteries in accordance with the
present invention were constructed using the
configuration shown in the illustrative embodiment.
Conventional Group 22 containers were used, modified to
provide ribs or shoulders 48 as generally shown in
FIG. 2.
The positive grids were cast from an antimony-lead
alloy having a nominal composition of, ~y weight, about
1.5~ antimony together with other alloying ingredients.
The nominal thickness of the grid was about 45 mils. A
standard positive active material paste formulation was
used, applied at a rate to yield about 2.5 grams of dry
active material precursor per square inch. Each grid
had a height of 4.5 inches, a width of 1.17 inches and
a weight of about 10 grams.
The negative grids were cast from an alloy having
a nominal composition of, by weight, about 0.12
calcium, 0.3% tin, and the remainder lead. The
nominal thickness was about 45 mils. A standard
negative active material paste formulation was used,
~ 173~
applied at a rate to yield of about 2.5 grams of dry
active material precursor per square inch~ The height,
width and weight of the negative grids were the same as
the positive grids.
The separator used was a commercially available
"Daramic"~silica-polyethylene material with a nominal
10 mil thickness, a resistance of about 8 to 12
milliohm-in.2, and with ribs to provide a spacing of
about 37 mils between the positive and negative plates.
A continuous strip of separator material was used for
each cell, folded in an accordion fashion as shown in
FIG. 1.
Twenty-eight positive and twenty-eight negative
electrode plates were used per cell. Sulfuric acid
electrolyte of 1.265 full charge spe~ific gravity was
included.
These batteries were subjected to conventional
Reserve Capacity and 0F. Cold Performance tests. The
resulting 0F. performance characteristics are set
forth in Table 1, the values being those for a 90%
compliance level and compared to those same values for
commercially available, maintenance-free batteries:
TABLE l
Ex. 1 Commercial Commercial
Battery Group 2~ Group 22
Reserve Capacity (Minutes) 70 110 76
Peak Power* 7156 5166 4278
Peak Power Watts/in.3* 15.4 8.9 9.2
Peak Power Watts/lb.* 235 121 138
30 Cold Cranking Amps
(nominal rating) 560 550 435
Cold Crank-Amps/lb. 18.4 12.9 14.0
Cold Crank-Amps/in.3 1.2 0.95 0.94
~ t~3~9'7
31
ResistanCe-weight e~uiva-
lent-milliohm-lbs~ 3.9 7O6 6.7
Resistance-lead weight
equivalent-milliohm-lbs. 2.3 4.7 4.0
*calculated by using measured internal resistance
The batteries of the present invention thus
provide cold crank performance which exceeds, based
upon the weight and size of the container volume or
cube, that of the Commercial Group 24 batteries. Gross
weight reduction of about 12.1 pounds and a volume
reduction of about 113 cubic inches is provided. More-
over, the peak power output is substantially improved;
and this would indicate that the starting power of the
batteries of this invention should be substantially
superior even though the nominal cold cranking ratings
are virtually the same.
While there are no weight or volume differences
when compared with the conventional Group 22 batteries,
the nominal cold cranking rating of the present
invention is markedly increased (560 vs. 435 amp).
Comparison of the Pea~ Power (7156 watts vs. 4288
watts) likewise shows the substantially improved
performance.
EXAMPLE 2
Batteries similar to that in Example 1 were
constructed, except that a total of 72 electrode
plates per cell were used, providing a more optimum
configuration for the size container employed. The
batteries were tested as in Example 1. The total
battery weights were each about 35.5 pounds.
Table 2 sets forth the 90% compliance levels for
the batteries tested:
l 173~7
32
TABLE 2
Reserve Capacity (Minutes) 92
BCI Cold Crank-Amps 735
Peak Power-Watts* 9171
Peak Power Watts/in.3* 19 8
Peak Power Watts/lb.* 258
Cold Crank-Amps/lb. 20.7
Cold Crank-Amps/in.3 1.58
Resistance-weight equivalent
-milliohm-lbs. 3.56
Resistance-Lead weight
equivalent-milliohm-lbs. 2.33
*calculated by using measured internal resistance
By comparison with the less than optimum design
shown in Example 1, the results set forth for the
batteries in this Example further demonstrate the
substantial improvements which can be obtained when an
optimized configuration is used.
The improved performance capable of being achieved
by use of the present invention can be further
illustrated by comparing, for various SAE battery group
sizes, batteries made in accordance with this
invention to batteries considered by the assignee of
this invention as being their present top-of-the-line, !~
conventional design, maintenance-free batteries.
Table 3 below sets forth this comparison, "CCA"
representing the nominal cold cranking rating in amps
"WT." being the gross weight of the battery and
"AMPS/LB." being the quotient obtained by dividing the
first two values:
3 ~ (3 ~
TABLE 3
~TTERY OF PRESENT IN~E~rIOM
PRESENT CCNSTRUCllON OPTIMIZED OONFIGURATIoN* EQUIVAlENT
SAE WEIGHT
GRD~P CCA WT. ~S/LB. CX~ WT. AMPS/LB. OONFIGURATION**
21 350 29.8 11.75 670 35.2 19.03 475
22 435 32.2 13.51 7~!0 37~6 19.15 515
24 550 41.5 13.2S 850 45.4 18.72 665
27 610 48.0 12.71 980 51.8 18.92 770
41 620 41.7 14.~7 800 42.5 18l~2 670
42 380 29.6 12.~3 600 32.6 18.4 475
54 310 25.1 12.35 ~70 30~6 18.63 400
380 30.2 12.58 640 34.7 18.44 485
56 ~50 35.8 12.57 730 41.2 17.72 575
57 310 26.3 11.78 550 29.2 18.84 420
58 41~ 32.2 12.73 600 33.3 18.02 515
61 310 27.8 11.15 600 32~ 18.4 445
62 380 32.2 11.80 670 37.0 18.11 515
63 450 3B.4 11~72 760 44.0 17.27 615
64 535 44.6 11.99 880 50.0 17.6 715
71 390 31.6 12.34 670 35.2 19.03 505
72 435 32.2 13.5 720 37.6 i9.15 515
73 480 36.2 13.26 750 38.9 19.28 580
74 550 41.3 13.31 850 45.4 18.72 660
77 610 47.8 12076 980 51.8 1~.92 765
*~enotes that the cell element is sized to snugly fit in the container
as previously described herein.
**Nominal cold cranking in amps based upDn a configuration having ~he
same weight as the p~esent construction hatteries, viz.-the rating was
calculated by multiplying the weight of the PRESENT CONSTRUCTION batte~y
by 16 a~ps/pound (considered to he easily achievable performanoe using
the present invention)~
's
7 3 '~ 3 7
3~
Table 3 shows the significant improvement obtained
by using the present invention, whether an optimized
configuration is used or a configuration of the same
weight is employed. Indeed, significant weight
reductions can be achieved by decreasing the number of
plates per cell employed, to about 40 or so, while
still providing satisfactory cranking performance. It
may even be satisfactory for some applications to
utilize cells having as few as 30 plates per cell or
so, perhaps as few as about 24.
The total number of plates per cell employed may
generally be dictated by the reserve and ampere~hour
capacities desired. Utilizing more plates will like-
wise increase the nominal Battery Council International
(BCI) cold cranking rating and peak power value but
should not significantly alter the cold crank amps and
peak power per unit weight or volume that will be
achieved.
Thus, as has been seen, the present invention
provides a battery with substantially improved power
characteristics to weight or volume ratio in comparison
to conventional SLI batteries. Yet, such batteries can
be constructed by utilizing, i~ desired, many of the
conventional battery assembly techniques. Indeed, the
batteries of this invention are accordingly amenable to
high volume production on a commercially attractive
basis.
