Note: Descriptions are shown in the official language in which they were submitted.
~ ~t~ L3
SE~LED, M~l~laNCE-F~;~;, LE~ACID B~ERIES
FOR FL~r APPI~:CATIOI~S
This invention relates to lead-acid batteries,
and, more particularly, to sealed, maintenance-free,
lead-acid batteries; capable of use for float applica-
tions such as automotive starting, lighting and igni-
tion applications.
For many applications, the trend in lead-acid
technology is to provide batteries which are mainten-
ance-free, i.e.~ - a type of battery which may be
operated without adding water to the electrolyte during
its recommended life. The life of such batteries is
limited by the water loss due to gas evolution; and,
therefore, excess electrolyte must be used to
3~3
--2--
compensate for the wat~r loss which occurs so as to
provide a satisfactory life.
Typically, such batteries have minimi~ed the loss
of water by using grid alloys haviny high hydrogen
overpotential. Rigid, self-supporting, and sometimes
structurally reinforced grids may be employed, made
from a variety of either antimony-free, or low-anti-
mony, lead alloys. Examples of grid alloy systems used
include calcium-lead, calcium-tin-lead, cadmium-antimony-
lead, selenium-antimony-tin-lead with various optional
alloying ingredients such as silver and arsenic as well
as combinations of these alloys.
Further, lead-acid batteries in which the electro-
lyte is immobilized in a gel form are known. Such
batteries can provide not only maintenance-free but
also spill-free characteristics, viz. - the battery may
be used in any attitude without electrolyte leakage.
However, the cracks which develop in the gel during
-; charge, while essential for oxygen transport, result in
conditions which can adversely affect the desired
performance. Also, such batteries invariably are
characterized by higher internal resistance and, hence,
cannot be used in applications where high rate discharge
capability is a requirement, such as, for example, an
automotive starting, lighting and ignition battery.
To provide a sealed design yet avoid the potential
problems with gelled electrolytes, sealed systems have
been utilized in which electrolyte is immobilized and
absorbed in special separators. The separators are not
fully saturated, and the gases evolved during over-
charge or at other times can diffuse rapidly from one
electrode to the other. Thus, under the right
~d~ 3
conditions, the oxygen that is evolved at the positive
electrode can diffuse to the negative electrode where
it will rapidly react with active lead. Effectively,
this reaction partially discharges the negative elec-
trode, preventing the negative electrode from reachingits full~-charged state so as to minimize the evolution
o~ hydrogen. This sequence results in what has been
termed an "oxygen cycle". While the oxygen recom-
bination rate is greater than the rate of oxygen being
produced at the positive electrode, there should be
minimal water loss and pressure build-up.
At the present time, sealed lead-acid systems of
this type have been available commercially in only
small ampere-hour capacity sizes. Usage has thus been
generally confined to standby applications such as
emergency lighting, alarm systems and limited cycle
life portable equipment such as television, lanterns
and garden tools.
U.S. 3,862,861 to McClelland and Devitt is an
example of a cell configuration recombining oxygen
using relatively high internal pressures. The cell is
thus said to enhance the rate of recombination by
operating under increased pressure. For this reason, a
vent relief is used which should be biased to vent at
as high a pressure as possible. A Bunsen-type relief
valve capable of retaining at least 10 to 15 pounds of
internal pressure is disclosed. This type of cell can
be used in float applications and in deep cycle applica-
tions in which limited life is acceptable.
A cell having a prismatic container is described
in Progress in Batteries & Solar Cells, Vol~ 2, 1979,
. .
~ 3L7~ 3
pp. 167-170, and is a type which apparently operates at
relatively iow internal pressures. This type is used
primarily for float applications.
A further type of battery is reported in the
International Symposlum on Batteries, October 21-23,
1958. As described, in general terms, the batteries
are made by building a stack of plates and flat, soft-
ish separators, the stack, after compression, being
~ inserted into a suitable container. In this stack or
block of plates and separators, the active material of
the plates is fully supported by the separators. The
block, after compression, must have a high enough
porosity to allow it to absorb and hold all the
electrolyte required for efficient and economic func-
tioning. The separators are made from diatomaceousearth. Batteries suitable for automotive starting,
lighting and ignition applications are disclosed, the
advantages described being resistance to vibration,
unspillability, and increased high rate performance at
normal and low temperatures. While the report des-
cribes the wide introduction onto the market as having
been limited due to commercial considerations rather
than to performance or quality, it is believed that the
performance characteristics do not meet present
requirements for such applications. Regardless, the
type of battery described has not achieved widespread
usage and has not been commercially successful.
Still further, it has been suggested that a sealed,
lead-acid system might be scaled up to iarger ampere-
hour capacity sizes than are being used commercially atthe present time (~ ering, October, 1978, The A~e of
the Sealed Battery, pp. 1020-22). It was, indeed,
.
~ 3~ ~ 3
stated that the characteristics of the sealed battery
system would be particularly advantageous for an auto-
motive SLI (viz. - starting, lighting and ignition)
application.
In addition to this application, there are a
number of what may be termed "float-pulse" applications
(viz. - a system capable of providing relatively high
peak power at fairly high discharge rates for brief
periods of time) where characteristics attributed to a
sealed system would seem to make such a system desir-
able for use. Batteries for motorcycles, starting
outboard motors and standby power for computers are
examples which fall into the category. Applications
reguiring a relatively pure form of direct current also
have similar requirements. Batteries for such applica-
tions require at least 15 ampere-hour capacities, or
evên 25 ampere-hours and substantially more.
Yet, for whatever reason, sealed systems of these
capacity sizes have not become commercially available
to any extent. It may well be that the necessary
performance characteristics have simply not been capable
of being provided. One may thus speculate that it has
proven difficult at best to achieve the capacity and
life needed for such applications. Also, it may be
felt that a stronger, more rigid battery container is
required to withstand the high internal pressures
believed necessary to provide satisfactory oxygen
recombination efficiency and that this would be partic-
ularly acute in batteries of relatively large capacity
sizes. The use of such stronger battery containers
would, of course, result in an increased weight for the
battery. This would be particularly detrimental in the
3~
automotive area since the present trend is to provide
battery systems in which the weight can be decreased as
much as possible.
It is accordingly a principal object of the pres-
ent invention to provide a sealed maintenance-free,
lead-acid battery which is capable of providing perfor-
mance characteristics satisfactory for use in float-
pulse applications.
Another and more specific object of this invention
provides a sealed, lead-acid battery capable of perfor-
mance which equals or exceeds the characteristics
required of batteries for automotive starting, lighting
and ig~ition applications.
A further object lies in the provision of a sealed,
lead-acid battery characterized by improved volumetric
and gravimetric energy density.
A still further object of the presen~ invention is
to provide a sealed, lead-acid battery which can be
designed in sizes ranging from small to extremely high
capaci-ties.
Yet another object lies in the provision of a
sealed, lead-acid battery capable of being manufactured
with standard equipment used for conventional float-
pulse battery production.
A still further object of the present invention is
to provide a sealed, lead-acid battery capable of using
the standard, thinwall plastic containers often employ-
ed for float-pulse batteries.
Another object of this invention provides a sealed
lead-acid battery capable of operation at extremely low
internal pressure yet providing maintenance-free charac-
teristics over an extended life.
~.~ 7~3
--7--
Other objects and advantages of the present inven-
tion will be seen from the following description and
the drawings, in which:
FIGURE 1 is a perspective view of a battery made
in accordance with the present invention, partially
cut-away to show the internal configuration;
FIG. 2 is an exploded, sectioned side ele~ation
view and illustrating the arrangement of the plates and
separators of the battery of the present invention;
FIG. 3 is a cross-sectional view taken generally
along line 3-3 of FIGURE 1, and further showing the
internal configuration of the battery;
FIG. 4 is a graph of voltage versus time and
showing the improved cold cranking behavior with a
sealed lead-acid battery made in accordance with the
present invention in comparison to a commercial mainten-
ance-free battery; and
FIG. 5 is a graph illustrating the performance of
a sealed, lead-acid battery of the present invention in
an industry cycle life test.
While the present invention is susceptible to
various modifications and alternative forms, there is
shown in the drawings and will herein be described in
detail, the preferred embodiments. It is to be under-
stood, however that it is not intended to limit the
invention to the specific forms disclosed. On thecontrary, it is intended to cover all modifications and
alternative forms falling within ~he spirit and scope
of the present invention as expressed in the appended
claims. Thus, while the present invention will be
principally described in conjunction with an automotive
starting, lighting and ignition a~plication, it should
~7~
be appre~iated that the present invention may be util-
ized for any other float-pulse application. Further,
th~ invention is, of course, equally applicable to
either a battery or to a single cell. Also, while the
present invention will be described in connection with
batteries of larger capacity sizes, it should be appre-
ciated that it is li~ewise useful in providing small
capacity sizes as well. Likewise, while all of the
advantages of this invention will not be obtained, a
container more rigid than that reguired by the internal
pressures developed in service can be employed, if
desired.
In general, the present invention is predicated on
the discovery that a sealed, maintenance-free, lead-
acid battery suitable for various float applicationssuch as, for example, an automotive starting, lighting
and ignition application, can be provided by immo~iliz-
ing the electrolyte in highly absorbent separators
while operating at extremely low internal pressures,
allowing use of conventional, thinwall containers. The
battery of the present invention will provide superior
peak power at relatively high discharge rates in compari-
son to conventionally used flooded electrolyte-type
batteries as well as satisfying the other performance
characteristics required.
Turning now to the drawings, FIGs. 1 and 2 show
the battery 10 in accordance with the present inven-
tion. The battery 10 has a container 12, separated
into individual cells by internal partitions 14. In
each cell, a plurality of positive electrodes 16 and
negative electrodes 18 are separated by ahsorbent
separators 20.
The electrical connections necessary can be made
by any of the several techniques which are ~nown in the
art. The particular technique employed does not form a
part of the present invention. As shown, conductive
straps 22 join the electrodes together, and the inter-
cell connections are shown in FIG. 3. The straps 22 of
the end cells are connected to external terminals 24 by
conventional means.
As seen in FIGs. 1 and 3, release venting is
provided through manifolds 26 to low pressure, self-
resealing relief valves, such as, for example, bunsen
valves 28. While venting through a manifold in illus-
trated, individual cells could each be provided with a
relief valve if desired. On the other hand, a single
manifold for the six cells shown could be used or more
than two manifolds can be utilized.
The electrodes, 16 and 18, and separators 20
should be snugly fit within the cells, i.e. - the
electrodes and separators should stay in the assembled
condition when the container is inverted. The elec-
trodes can thus be sized to almost the interior dimen-
sions of the cells. To eliminate the possibility of
shorts, it is, however, desirable to size the separa-
tors used such that the edges extend slightly past all
of the edges of the electrodes, as is shown in FIG. 2.
One means of achieving this at the bottom of the elec-
. trodes is to fold the separators around the electrodewith a U-fold as depicted in FIG. 2.
Highly efficient use of the internal container is
obviously thus provded. However, if desired, spacing
means, such as shims, could be employed if the cells
employed are oversized for any reason.
~L7~3
--10--
Considering the present invention in greater
detail, the grids used for the positive and negative
grids can be any of the several known grid alloys used
for conventional maintenance-free batteries. As one
S example, it is thus suitable to utilize a calcium-tin-
alloy in which the calcium content is from about 0.06
to 0.20% and the tin is in the range of 0.1 to 0.5%
(preferably 0.2-0.3), both percentages being based upon
the total weight of the alloy. The alloys used should
be capable of providing self~supporting grids. The
grids may be formed by any of the known techniques,
such as direct casting or expanded metal.
There are several difficulties associated with
providiny a satisfactory internal structure for a
sealed system. One such difficulty arises from the
need to provide an absorptive capacity for the system
to insure that sufficient electrolyte will be retained
to yield the desired capacity. This can be provided to
some extent by using thicker separators than would be
needed for a flooded - electrolyte system. However,
this will generally not be a complete answer as the
internal resistance will increase as the plate spacing
is increased. There is thus a practical limit in the
trade-off of performance characteristics which will
result. Some benefit can be obtained by using somewhat
higher specific gravity electrolyte than conventional
flooded systems; but, here too, there is a practical
upper limit due to factors such as the decreased con-
ductivity which results. A further possibility is, of
course to decrease the density of the active material
pastes. Since mossing of the negati~e active material
and shedding of the positive active material should be
--11~
prevented, or at least substantially minimized, by the
snug fit of the electrodes within the absorbent separa-
tors utilized, lowering the active material paste
density should conceptually be possible. However, here
again, there are limitations because of processing
problems which arise with such reduced densities whPn
conventional pasting machines are employed, as in an
automotive application.
A further difficulty arises from the shrinkage in
the negative active material which occurs in batteries
exposed to float conditions, as is known. This can be
a primary mode of failure, significantly lessening the
useful life of a battery. It is for this reason that
battery manufacturers have conventionally used various
expanders to maintain the desired porosity and active
material surface area of the negative plates. It has
been found that this difficulty is particularly acute
in sealed systems for float applications.
Accordingly, to obtain all of the advantages of
the present invention, it is preferred to utilize
active material pastes which have increased absorptive
capacity yet which can be readily processed with conven-
tional equipment and provide a system with satisfactory
life and performance characteristics. To this end, the
paste densities for the positive active materials are
lower than the paste densities used for conventional,
flooded, lead-acid batteries using long life, leady-
oxide materials, such as those obtained from a Barton
pot. It has thus been found suitable to utilize plate
densities in the range of from about 2.9 to 4.1 grams/
cm.3 for the cured, unformed positive active material.
13~
-12~
A density range of 3.0 to 4.2 grams/cm.3 for the cured
and formed positive active material is acceptable.
To provide the desired electrolyte retention
properties, it is preferred to incorporate an electro-
lyte-retaining agent such as colloidal silica into the
paste. Incorporation of colloidal silica in an amount
of from about 0.05-1.0%, based upon the weight of the
unformed positive active material, has been found suit-
~ able. Other electrolyte-re~aining materials are known
and may be similarly utilized as substitutes, in whole
or in part, for the silica. Desirably, the electro-
lyte-retaining agent should also function as a bulking
agent, viz. - increase the consistency o the wet paste
so as to improve handleability. Colloidal silica
satisfies this function.
In accordance with a further and preferred aspect
of the present invention, the characteristics of the
negative active material is enhanced not only to in-
crease the absorptive capacity but also to compensate
for the effects of shallow cycling to provide satisfac-
tory life and performance characteristics. To this
end, the negative active paste preferably includes a
combinat:ion of conventionally used paste additives
abo~e the levels typically used. As one component, it
is preferred to utilize a conventional organic expander
at a level of from about 0.3 to about 1.0%, based upon
the weight of the dry, unformed paste. Various ligno-
sulfonates such as, for example, sodium lignosulfonate
are known and are suitable. In addition, it is pre-
ferred to utilize an additive serving to minimize thephysical consolidation of the lead sulfate crystals
formed during cycling into larger crystals and
~7~ 3
eventually into an essentially solid layer with minimal
porosity, ~esulting in failure of the battery. Cellulose
floc serves this purpose, and a level of about 0.3 to
about 1.0% by weight may be used.
It is not believed that the maximum benefits will
be achieved by utilizing only one type of expander as
the functions are believed different. In some fashion,
the organic expander affects the morphology of the lead
~ sulfate structure to retard loss of porosity. The
additive which retards consolidation is believed to
serve, in effect as a physical spacing means.
Preferably, the paste additives utilized should
likewise function as bulking agents for the paste.
Cellulose floc and sodium lignosulfonate both serve
this function.
A mixture of 0.75% sodium lignosulfate and 0.6%
cellulose floc, both percent^age being based upon the
weight of the dried unformed pastè, is preferred. Use
of this mixture appears to provide the desired cycle
life.
The cured, but unformed, paste density for the
negative active material should desirably be in the
range of about 3.5 to 4.4 grams/cm.3. A density range
of about 3.2 to 4.1 grams/cm.3 for the cured and formed
negative active material is satisfactory. While the
negative paste additives previously described serve to
retard loss of porosity and thus retain the absorptive
capacity, it is preferred to also incorporate in the
negative paste an electrolyte-retaining agent such as
colloidal silica. Amounts in the range of from about
0.05 to 1.0~, based upon the weight of the dried,
unformed paste are suitable.
-14-
It has typically been believed essential, as set
forth in ~.S. 3,862,8~1, to utilize in a sealed system
an excess of negative active material in relation to
the positive active material so that the re~uisite
oxygen cycle will be attained. According to one aspect
of the present invention, it has been found that a
satisfactory oxygen cycle will be achieved even though
the amount of negative active material is less than
that of the positive active material. It is accordingly
preferred to utilize a negative active material to
positive active material weight ratio of from about
0.75 to about 0.92, or so. This results in not only
reduced weight but also in less cost without detrimental
effects on performance.
The material used for the separators 20 should be
stable in the sulfuric acid electrolyte used, resistant
to oxidation by PbO2 and not release materials into the
electrolyte which would deleteriously affect cell per-
formance. In addition, the material should be highly
porous, e.g. - at least 70 to 75%, desirably up to
about 90% or so, and should be sufficiently co~pressible
to at least substantially conform to the changing
shapes of the electrodes during assembly and service.
Further, average pore diameter should be sufficiently
small to prevent propagation of dendrites from the
negative plate and shedding of the active material from
the positive plate. The average pore diameter should,
however, be suf~iciently large to be easily wetted by
the electrolyte and not so small as to result in an
unduly high internal impedance. The separator material
must also be capable of wicking the electrolyte through
the desired height of the separator.
~ 3~ 3
-15-
Lastl~, and importantly, the separator material
must pre~erably provide, in service, a substantially
uniform void volume throughout the separator. The
separator thus preferably provides sufficient void
volume to support the rate of oxygen transport neces-
sary for the internal pressure desired for the cell.
It is believed that the void volume is achieved through
some of the pores having their walls covered with a
film of electrolyte while the central portion of the
pore is free from electrolyte. Satisfactory oxygen
recombination efficiency for some applications may be
achieved even when the separa~or is thoroughly wetted
with electrolyte. 5uitability in this respect can be
determined by weight loss (water) determinations made
during cycling. Unduly high water loss should not
result if the material is suitable.
The thickness of the separator will, in general,
be determined by the cell capacity and the expected
operating rate for the particular application. In this
respect, the separator thickness used does not mater
ially differ from those found suitable for other types
of lead-acid cells used for the particular end usP
application.
It has been found suitable to use a borosilicate
glass material formed from glass microfibers and chopped
strands. Materials of this type are commercially
available and have been previously utilized for sealed,
lead-acid cells. One such material (C.H. Dexter
Division, The Dexter Corporation, Windsor Locks,
Connecticut, "Grade 225B") that has been found satis-
factory has the following typical properties: nominal
thickness of 300 microns, air permeability (ASTMD737-?5)
L3
of 15.1 1/min/100 cm.2 at ~2.7 mm. water ~ P ~Frazier
Permeometer), an average pore size of 12.6 microns and
a porosity (by mercury intrusion) of 1.2 meters2/gram.
It is preferred to utilize at least one layer of
the glass borosilicate material adjacent the elec-
trodes. Additional layers of other materials may be
used, as for example, for reinforcement to improve
handleability in processing. As illustrative examples,
~ commercially available, nonwoven, polyethylene, polypro-
pylene and polyester sheets may be suitably employed.
Such materials possess the desired electrolyte retention
but both provide decreased cost as well as improved
strength. Such a laminar separator system can be used
to provide the necessary strength for relatively easy
introduction of pocket-type and U-fold separators in
conventionally used, high feed, SLI battery assembly
techniques. ;
For a given application, the full charge specific
gravity for the electrolyte needed can be readily
computed. Typically, full charge specific gravities in
the range of 1.255 to 1.320 will be satisfactory, 1.285
to 1.320 being preferred. Particular applications may
make it desirable to use somewhat higher or lower acid
gravities.
The formation of the pasted electrodes can be
carried out by known techniques. Thus, prior to assem-
bly in the container, the electrodes can be formed by
conventional tank formation. When this technique is
employed, the formed electrodes should be dried to
remove the residual electrolyte.
Desirably, however, the unformed electrodes and
separators are placed in the container, the necessary
'o~ .3
-17-
electrical connections made, the cover sealed to the
container, the necessary electrolyte added through the
aperture in the cover for the relief valve, and the
valve then put in service position~ Formation is then
carried out using conditions suitable for conventional
one-shot, lead-acid battery formation. It may be
useful, however, to employ somewhat less severe forma-
tion finishing conditions than those conventionally
used. It may also be desirable to initially chill the
formation electrolyte to some extent.
It should likewise be noted that, when in situ
formation is employed, initiation of formation should
take place within about 1/2 to 1 hour or so after the
electrolyte is added. Longer delays can result in
conditions which may ultimately create internal shorts
The amount of electrolyte employed should prefer-
ably not result in the absorbent materials of the
battery being fully saturated, i.e~ - the hattery
should be in an electrolyte-starved condition. While
the battery in service is self-regulating, a fully
saturated condition may result in undue gassing during
the initial stages of charging during cyclic operation
Further operation will reach an equilibrium state where
an efficient oxygen recombination cycle is achieved.
The somewhat higher gassing which occurs during the
initial stages can be substantially eliminated by
determining the particular void volume reguired for
efficient oxygen recombination. ~owever, it has b~en
found suitable to add electrolyte sufficient to satur-
ate the absorbent capacity of the system to a level ofabout 90%.
~7~3
-18-
Care should be taken to avoid free electrolyte in
the system. Significant quantities of free electrolyte
(viz. - not immobilized in the electrolyte and separa-
tors) can adversely effect performance.
In accordance with one aspect of the present
invention, release venting is provided by a self-reseal-
ing relief valve which unseals at extremely low internal
pressures. To this end, a valve is employed which will
unseal at internal pressures of from about 0.5 to about
3.0 psig. Indeed, it is preferred to utilize internal
operating pressures of no more than about 1 or perhaps
; 2 psig so that conventionally used, thinwall, plastic
containers may be employed.
The following Examples further illustrate, but are
not in limitation of, the present invention. Unless
otherwise specified, all percentages are by weight.
~t
EXAMPLE 1
This Example illustrates the performance of the
sealed lead-acid battery of the present invention in
comparison to a conventional, flooded, maintenance-free
battery.
Batteries of a nominal ampere-hour capacity of
about 71 were assembled in hard rubber containers.
Each battery contained 17 plates per cell. The alloys
used for the grids of both batteries were calcium-tin-
lead having a nominal composition of 0.09% calcium,
0.3% tin and the remainder lead. The paste densities
employed were 4.0 gms./cm.3 for the positive and 4.4
for the negative, both based upon the dried, unformed
paste weight. The pastes were cured by exposure at
140F. for about 16 hours in a 100% relative humidity
~7~
--19--
atmosphere, followed by exposure at 140F. to a zero
percent relative humidity atmosphere for a period of
about 48 hours or so. Each electrode of the battery of
the
present invention was wrapped with a two-layer separa-
tor comprising an interior layer of a nominal 13 mil of
the borosilicate glass material previously described
and a 13 m~l exterior layer of a nonwoven, point-bonded
~ polypropylene material, U-folded about the electrode as
depicted in FIG. 2. A conventional polyvinylchloride
separator having a nominal thickness of 37 mils with a
12 mil back web was used for the conventional mainten-
ance free battery.
Other constructional details are set forth in
15 Table 1:
Table 1
SealedConventional
20 Parameter Battery Battery
Positive grid thickness, inches0.041 0.041
Negative grid thicknessl inches0.039 0.039
Dry positive paste weight pe~ 110 110
plate, gms.
Dry negative paste weight per 101 101
plate, gms.
Ratio of positive paste wt./grid 70/40 70/40
wt., gms.
30 Ratio of negative paste wt./grid62.5/38.5 62.5/38.5
wt., g~s.
Specific gravity of electrolyte 1.285 1.285
Interplate spacing, inches0.022 0.037
7~3~3
-20-
Further details of the overall batteries are set
forth in Table 2.
Table 2
SealedConventional
Parameter Batterv Battery
Total wt., positive paste, lbs. 7.40 7.40
10 Total wt., negative paste, lbs. 7.44 7.44
Total wt., positive grids, lbs. 4.23 4.23
Total wt., negative grids, lbs. 4.58 4.58
Total wt., lead within element, 23.65 23.65
lbs.
15 Total wt. of electrolyte, lbs. 5.75 15.30
The plates and separators were placed in the
containers, the necessary electrical connections made,
and formation acid of 1.200 specific gravity cooled to
20 0F. added. A charge regime of 7 amps for 16-lt2
hours, followed by 4 amps for 3 hours and ~ amps for 2
hours, was used. The covers were then put in position.
The sealed battery included a conventional Bunsen
relief valve which unsealed at 0.5 psig.
The batteries were then tested and the performance
is set forth in Table 3:
,
~'7~
--21--
Tabl e 3
Sealed Conventional
Test Battery Battery
s
0F. Cold crank, voltage 8.05 7.60
after 30 sec., 550 Amps
Relative electrical resist- 9.9 11.2
ance, 0F.
Reserve capacity, 25 Amp 78 124
discharge, minutes
As can be seen, the sealed battery of the present
invention provides better cold-cranking power than the
conventional maintenance-free battery. FIG. 4 also
shows this improved performance over the 60 second
discharge to which each battery was subjected, the
curve labelled 1 being the sealed system and curve 2
being for the conventional, maintenance-free battery.
However, as seen from Table 3, the reserve capa-
city of the sealed battery of this invention was sub-
stantially lower than that of the conventional,
maintenance-free battery. It should be appreciated
that the active material pastes were not modified as
previously described, and the results thus highlight
the need for suitable modification to achieve all of
the advantages of this invention.
The sealed battery was subjected to a standard SLI
12 minute cycle, J240 regime and failed at about 4500
cycles which is substantially less than that typically
achieved by the performance of commercially available,
maintenance-free batteries. However, the failure mode
~.~i7~
-22-
was believed due to a design flaw in the particular
positive grids used.
EXAMPLE 2
This Example illustrates the life performance
capable of being achieved by a sealed battery made in
accordance with the present invention.
A test battery was assembled having a nominal
ampere-hour capacity of about 67 which contained 13
plates per cell. The alloys used were the same composi-
tion as set forth in Example 1. The cured, unformed
paste densities were about 4.4 gms./cm.3 for the neqa-
tive active material and about 3.9 for the positive
active material. The negative paste was made from a
formulation which included, in part, 1200 gms. of leady
litharge, 50 grams of a conventional expander mixture
and about 0.3% colloidal silica based upon the dry,
unformed weight of the paste.
The pastes were cured as described in EXAMPLE 1.
The positive plates were wrapped with 2 layers of the
borosilicate glass material previously described and
the negative plates were wrapped with a single layer of
that material.
The plates and separators were placed in a stand-
ard SLI, thinwall, plastic container used for commer-
cial, maintenance-free batteries, modified to substan-
tially reduce the height of the rest-ups in the bottom
of the container. Assembly and formation were carried
out as generally described in EXAMPLE 1, the specific
formation regime involvin~ charging at 7 amps for 18
hours, followed by 4 amps for 6 hours and 2 amps for 2
hours.
--23--
Other constructional details are set forth in
Table 4, the specifications for a conventional, mainten-
ance-free battery being inc]uded as a general compari-
son:
Table 4
Sealed Conventional
Parameter Battery Specification
Positive grid thickness, inches 0.075 0.064
Negative grid thickness, inches 0.051 0.047
Dry positive plate wt., gms. 148 149
Dry negative plate wt., gms. 104 107
15 Ratio of positive paste wt./grid 89.8/58.5 87/62
wt., gms.
Ratio of negative paste wt.~grid 63.5/40.2 66/41
wt., gms.
Specific gravity of electrolyte 1.290 1.265
Table 5 sets forth details of the assembled bat-
tery, the specifications for the conventional battery
referred to in conjunction with Table 4 also being
included:
~'7~
-24-
Table 5
Sealed Conventional
Parameter Battery Specification
Total wt., positiv~ paste, lbs. 7.12 6.90
Total wt., negative paste, lbs. 5.88 6.11
Total wt., positive grids, lbs. 5.42 4.92
Total wt., negative grids, lbs. 3.73 3.78
Total wt. within elements, lbs. 22.15 21.72
Total wt. of electrolyte, lbs. about about
6.90 11.60
Total wt. of battery, lbs. 32.2 37.8
The sealed battery was tested, and Table 6 sets
forth the results in comparison to the specifications
for the conventional battery described herein:
Table 6
Sealed Conventional
Test Battery Specification
0F. cold crank, volts at7.84 7.2
30 sec., 500 Amps discharge
Reserve capacity, 25 Amps, 91 102
mins.
As can be seen from Table 6, the sealed battery of
this invention provides the same improved cold cranking
as shown in EXAMPLE 1. Also, while still not the same
as the conventional battery, the modification to the
negative grids together with the increased interplate
3~3~3
--2s--
spacing has provided improvement in relation to the
comparison shown in EXAMPLE 1. Further improvsment in
this regard can be achieved by further modification of
the active material pastes as previously described.
The sealed battery was subjected to the J240 life
test described in EXAMPLE 1 and achieved about 8000
cycles. During this test regime, the battery was
discharged at 500 amps; and the 5-second and 30-second
voltages were ascertained. FIG~ 5 sets forth the
results, curve 3 being the 5-second and curve 4 being
the 30-second voltages. Failure occurred through
positive grid corrosion, considered to be a design
defect in such grids.
Significantly, over the life of the J240 test, the
sealed battery of this invention lost only about 0.15
lbs. of water (+ 0.05 accuracy in measurement~ which is
;considered to be about an order of magnitude less than
would be expected from a conventional, maintenance-free
battery.
Thus, as has been seen, the battery of the present
invention provides all of the advantages of a sealed
system and particularly provides improved peak power at
relatively high rates for the short times encountered
in a wide variety of float applications. In an automo-
tive starting, lighting and ignition application, this
invention thus provides significantly superior cold
cranking power. This performance is achieved while
maintaining the other performance characteristics
required. The efficient oxygen recombination rate even
at the extremely low internal pressures provides super-
ior maintenance-free characteristics. The use of low
internal pressures likewise allows the utilization of
.3
-26-
conventional, thinwall plastie containers, a highly
useful feature in automotive applications where reduced
weight is becoming more and more important. Indeed,
the relatively high volumetrie energy density eapable
of being aehieved ean allow the use of even smaller
sized eontainers with no sacxifice in performanee.
