Note: Descriptions are shown in the official language in which they were submitted.
3~3
M-IND-7 B 0 6
BACKGROUND OF T~E INVENTION
The present invention related to lead-acid bat-
teries and more particularly to improvements in gel
electrolytes and separator materials for use therein.
A gel may be regarded as a type of colloidal sys-
tem behaving as a solid of relatively low elasticity.
Various attempts have been made ~o gel the acidic elec--
trolyte in storage battery cells to eliminate spilling,
the need for constant main~enance and for other reasons.
No satisfactory gel electrolyte has been produced, how--
ever, because batteries containing such gel electrolytes
; have not had electrical properties as good as those with
ordinary liquid electrolytes. For example, ~heir inter-
nal resistance is higher and capacity is lower in bat-
teries incorporating a gel electrolyte. Alsol the cycling
characteristics of batteries containing the gel electro-
}yte have not compared well with batteries having liquid
electrolytes. In addition to these disadvantages, gel
electrolytes have had a tendency to shrink after a short
time so that the contact between the gel electrolyte and
the active mass in the bat~ery cell is soon interrupted.
Thus, cracks form i~ the gel- electrolyte allowing air to
carry oxygen to the plates or electrodes of the battery,
allowing the electrodes to discharge.
3~3
--2--
Furthermore, the initial viscosity of the gel is SQ
great that it has been difficultl if not impossible, to
completely fill the electrolyte chamber and the electrode
pores with the gel electrolyte.
One such attempt at gelling an elec~rolyte was dis-
closed in British Patent No. 785,848, issued to Robinson
on November 6, 1957. This patent discloses the use of
fine partic1es of silica of submicron size, approximately
0.015 micron diameter, mixed with dilute sulfuric acid.
The amount of silica in the final mixture is disclosed to
be about 12~ by weightO However, the problems described
above still remain.
Another problem which affects ~he use of both liquid
and gel electrolytes i5 the need to replace the electro-
lyte after formation of the cell. Presently, most lead-
acid batteries are filled with low specific gravity elec-
trolyte and the electrodes of the batteries are formed by
placing a charge on them. After this formation process,
the formation electrolyte is dumped out and is replaced
with resh electrolyte having the desired specific gravity.
It is well known that if the low specific gravity formation
electrolyte were not replaced, the battery would exhibit
poor electriral properites.
~he forma~ion process is expensive for a number OL
reasons. Changing electrolyte a~ter charging requires
additional labor and time. Even though the formation
electrolyte may be recycled, contaminants build Ip in
the electrolyte. Eventually, the electrolyte must be
either cleaned or discarded.
It is well known that separator material is placed
between electrodes of batteries to prevent electrical
shorting. Simultaneously, the separator material must
also permit diffusion of electrolyte through its pores
and the passage of ~lectric current between the electrodes
~ 15~3~3
; -3-
;
of batteries to prevent electrical shorting. Simul-
taneously, the separator material must also permit
diffusion of electrolyte throu~h its pores and the
passage of electric current between the electrodes.
Additionally, the separator material must be stable
in the electrochemical environment, i.e., resist
deterioration due to exposure to the electrolyte and
the chemical reactions taking place on the electrodes.
- One of the long standing problems in improving bat-
I0 teries has been to make a separator material which
optimized these various characteristics.
SUMMARY OF THE INVENTION
The present invention contemplates a gel electro-
lyte for use in a lead acid battery. The gel electro-
lyte includes a silica component having silica particles,
means for repelling the particles from each other and
for catalyzinq the for~ation of siloxane cross-linkages,
and a sulfuric acid component. Additionally, the present
invention includes a lead-acid battery incorporating the
gel electrolyte. The lead-acid battery includes a con-
tainer, a plurality of electrodes substantially enclosed
by the container, and the gel electrolyte in a substan-
tial physical contact with the plurality of electrodes.
A separator material for a lead-acid battery is
also included in this invention. The separator material
includes a silicate component integrally mixed with an
oxygen compound of boron forming a microfiber mat. The
mat has a pore si~e between about 0.5 to 10 microns in
diameter and an electrical resistance of about 0.01 ohms
per square inch for a 0.0S inch thickness. Additionally,
the present invention includes a lead-acid bat~ery which
~tilizes this separator material. Specifically, the
battery includes a container, a plurality of electrodes
.
1 1583~3
" .
'r, ~f--electrodes substantially enclosed by the container,
an electrolyte in substantial physical contact with the
plurality of electrodes, and a separator material in
physical contact with and substantially enveloping at
least one of the electrodes.
This invention also encompasses a method of making
a l~ad-acid battery having electrodes disposed in a con-
tainer. The steps of this method include filling the
electrolyte space of the battery with an electrolyte.
Subsequently, the battery is substantially sealed and
he electrodes of the battery are formed. Thus, the
electrolyte is retained in the ba~tery as the operational
electrolyte.
Another method of making a lead-acid battery having
electrodes disposed in a container is included in the
present invention. The steps of this method include
enveloping an electrode of the battery with a separator
mixed with an oxygen compound of boron forming a micro-
fiber mat. The mat has a pore size batween about 0.5
to 10 microns in diameter and electrical resistance of
about 0~01 ohms per square inch for a 0.05 inch thickness~
It is an object of the present invention ~o provide
an electrolyte which can be used in situ for both the
electrode as well as for battery service.
It is another object of this invention to provide
an electrolyte which is economical to manufacture anduse in lead-acid batteries. Still another object of this invention is to pro-
vide an electrolyte which eliminates the additional time
and expense required to change electrolyte after the
formation process.
A further object of this invention is to provide an
electrolyte which reduces gassing of the battery electrodes
during cycling as compared to prior art cells.
1 :~5~3~3
5--
A still further object of ~his invention is to
provide a gel electrolyte which eliminates the need
for constant maintenance during the life of the bat-
tery.
Ano~her object of the present invention is to
provide a gel electrolyte which improves the capacity
of a battery.
Still another object of this invention is to pxo-
vide a gel electrolyte which eliminates the possibility
10 of spillins the electrolyte from a battery.
A further object of this invention is to provide
a gel elec~rolyte which improves the cycle life of a
battery compared to prior art cells.
A still further object of this invention is to
provide a gel electrolyte which serves as a separator
between the electrodes of a battery.
A~other object of this invention is to provide a
separatox matexial which improves the capacity of the
battery.
Still another object of the present invention is
to provide a separator materlal which improves the cycle
life of the battery.
A further object of this invention is to provide a
separator material which is easily and conveniently dis-
posed in contact with the electrodes of a battery.
For a better understanding of the presen~ invention,
together with other and further objects thereof, refer-
ence i5 had to the following description, taken in con-
nection with the accompanying figures, while its scope
will be pointed out in the appended claims.
~ 15~303
--6--
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of a battery uti
lizing sepaxator material of the present invention.
~ igure 2 depicts the setting time of variou~ mix-
tures of gel electrolytes included in the present in-
vention.
Figure 3 depicts ~he results of a penetrationtest on various mixtures of gel electroly~es included
in the present invention.
Figure 4 is a compilation of the capacities after
discharge at the 6-hour rate of two groups of cells
utilizing the present invention in comparison with
conventional cells representing the prior art.
Figure 5 compares the battery cells utilizing the
present invention with conventional cells representing
lS the prior art in xegard to cell voltage and positive
electrode potentials at the end of formation.
Figure 6 compares battery cells utilizing the
present invention with conven~ional cells representing
the prior art in regard to negative electrode potentials
at the end of the formation measured against Cd/CdSO4.
Figure 7 shows a comparison of battery cells uti-
lizing the present invention with conventional cells
representing the prior art in regard to the percentage
of rated capacity against different rates of discharge.
Pigure 8 compares battery cells utilizing the
present invention with conventional cells representing
the prior ar~ in regard to the percentage of rate~-lcapa~
city at the 6-hour rate of discharge against the number
of cycles.
Figure 9 compares battery cells utilizing the
present invention with conventional cells representing
the prior art in regard to the percentage of rated
~5~3~3
capacity at the l hour rate of discharge ayainst the
number of cycles.
Figure 10 compares battery cells of the present
invention with conventional cells representing the prior
art in regard ~o the gas evolution against percentage of
chargeback of the discharge capacity.
Figure 11 compares battery cells utilizing the
present invention with conven~ional cells representing
the prior art in regard to the rate of gas evolution
against an extended period of overcharge.
Figure 12 compares battery cells utilizing the
present invention with conven~ional cells representing
the prior art in regard to the capacity performance
gainst the number of cycles.
Figure 13 depicts the capacity performance of bat~
tery cells, all of which are included in the present
invention, having gel electrolyte with and without
Dexiglas after different periods of cycling.
Figure 14 shows the cell voltages at the end of
chargeback for cells, all of which are included in the
present invention, having gel electrolyte with and
without Dexiglas after different periods of cycling.
Figure 15 shows positive electrode potentials at
the end of chargeback for cells, all of which are in-
cluded in the present invention, having gel electrolytewith and without Dexiglas a~ter different periods of
cycling.
Figure 16 shows negative electrode potentials at
the end of chargeback for cells, all o which are in-
cluded in the present invention, having gel electro-
lyte with and without ~exiglas after different periods
of cycling.
~ ~5~3~3
8--
Figure 17 depicts positive electrode potential~
at the end of discharge for cells, all of which are
included in the present invention, having gel electro-
ly~e with and without Dexiglas after diferent periods
of cycling.
Figure 18 shows negative electrode potentials at
the end of discharge for cells, all of which are in
cluded in the presen~ invention, having gel electrolyte
with and without Dexiglas after diferent periods of
cycling.
DETAILED DESCRIPTION OF THE INVElITION
The present invention contemplates an electrolyte
for a lead-acid battery which includes a silica compon~
; ent having silica particles, means for repelling the
particles from each other and catalyzing the formation
of siloxane cross-linkages, and a sulfuric acid compon-
ent.
Silica is the oxide of silicon, SiO2. Silica is
readily available commercially in numerous particle
si2es and used accordingly in the present invention.
; In the preferred embodiment, the silica particles are
less than about 1 micron in diameter. It should be
understood that this invention is not intended to be
limited by the amount of silica present in the elec-
trolyte. Although a~y a~ount of silica may be used,
a preferred embodiment has the silica component con-
stituting less than about 30% of the electrolyte's
weight. In a more preferred embodiment, the silica
component constitutes between about 1 to 7~ of the
electrolyte's weight.
~ ~S~3~
_9_
The sulfuric acid component in the electrolyte of
the preferred embodiment measures between about 30 ~o
50~ of the electrolyte'~ weight. This figure is cal-
culated using sulfuric acid having a specific gravity
of about 1.400 before mixing. A more preferred embodi-
ment measures the sulfuric acid component ~etween about43 to 48~ of the electrolyte's weight. Once again, this
figure is calculated using sulfuric acid having a spe-
cific gravity of 1.400 before mixing. An alternative
method of measuring the preferred amount of sulfuric
acid in the electrolyte is to measure the speciic
gravity after mixing the sulfuric acid into the elec-
trolyte. If this is done, the sulfuric acid componen~
should have a specific gravity o about 1.200 to 1.390
in ~he preferred embodiment of the electrolyte.
It should be understood that the present invention
contemplates use of the various means for repelling the
silica particles from each other and catalyzing the for-
mation of siloxane cross-linkages. The siloxane cross--
linkage is a compound of silicon and oxygen in which
each atom of silicon is bonded to four oxygen atoms,
forming a tetrahedral structure, in a manner analogous
to the honding of carbon to hydrogen in methane, the
bonds being of about the same strength in each case.
This structure is found in the dioxide and in silicates
generallyl where the SiO4 groups occur in chains or
rings. By creating siloxane cross-linkages, a gel is
formed.
The silica particles can be repelled from each o~her
by forming a liquid colloidal dispersion stabilized by
electric charges, either all negative or all positive,
whereas the particles are kept from colliding or floc-
culating by mutual electrical repulsion. A texm used
to describe this liquid colloidal dispersion is a so:L
s~ate. The sol s~ate is opposed to the gel state, in
which the dispersion is a thick, semisolid mass.
~ 1 5~3~3
One example of means for repelling the silica
particles from each other and catalyzing the formation
of siloxane cross-linkages is a plurality of hydroxyl
ions~ ~ydroxyl ions have two important effects Up~D
silica p~xticles: they react wîth surface silanol
groups on the ~ilica particles to create negatiVQ
surface charqes which cause the silica particles to
repel each other, ~hus inhibiting gel formation; and,
they also directly catalyze the formation of siloxane
~0 cross-linkages ~or gel formation. As the pH decreases,
such a~ upon the addition o sulfuric acid, particle
charge decreases but sufficient hydroxyl ions remain
to catalyze crsss-linking~ Thus, a gel is formed.
A preferred embodiment of the above mentioned means
is an alkali component. A more preferred embodiment of
the alkali componen~ is ~o select the alkalî from the
group consisting of ammonium hydroxide, sodium hydroxide,
and sodium aluminate. In the preferred embodiment, the
alkali component is less than about 5% of the electrolyte's
weight. In the more preferrea embodiment~ the alkali
component is less than about 1~ o~ the electrolyte's weight.
I~ should be understood that the invention contemplates
the use of other components ~esides the three mentioned
above. Other components listed for sake of examplet and
not intended as a limitation, are found in ~Properties,
Uses, Storage~ and Handling Ludox Colloidal Silica~ which
is published by E. I. duPont de Nemours ~ Company.
One such componet is salt. In the preferred embodi-
ment, the electrolyte includes a salt component selee~ed
from a group consisting o~ sodium chloride, ammonium
chloride, ammonium acetate, and ammonium nitrate. The
salt component in the preferred embodiment is less than
about S~ of the electrolyte's weight.
~ ~5~3~3
The electrolyte can further include a sulfate
component. In the preferred embodiment, the sulfate
component constitutes less than about 5% of the elec-
trolyte's weisht.
The abo~e mentioned electrolyte can be used in a
lead-acid battery. The battery includes a container
and a plurality of electrodes substantially enclosed
by the container. ~n electrolyte of this invention
is placed in substantial physical contact with the
plurality of electrodes. In should be understood tha~
various dimensions and types of con~ainers as well as
electrodes are contemplated for use in the present
invention.
The present invention also includes a separator
material for lead-acid battery. The separator ma-
terial includes a silicate component integrally mixed
with an oxygen compound of boron forming a microfiber
mat. The mat having a pore siæe between ahout 0.5 to
10 microns in diameter and an electrical resistance of
20 about 0 01 ohms per square inch for a 0.05 inch thick-
ness.
A si~icate is any of a broad range of mineral
compounds comprised of from one to six silica groups
(SiO2), arranged either in rings or chains. In a pre-
ferr~d embodiment, the silica component is more than
about 40% of the layer's weight. A more preferred
embodiment measures the silica component to be about
55 to 65% of the layer's weight.
The present invention contemplates the use of any
oxygen compound of boron. In a preferred embodiment,
the oxygen compound of boron measures about .5 to 15~
of the layer's weight. In a more preferred embodiment,
the oxygen compound of boron is selected rom the group
consisting of boron oxide and boric acid.
3 0 3
Al~hough the microfiber mat contemplated by this
invention may be of nearly any thickness, the preferred
embodiment is to have the layer measure about O.01 to
0.1 inches in thickness. In the more preferred embodi-
ments of the layer contemplated by the present invention,the electrical resistance is preferred to be as small as
possible. Whereas~ in the preferred embodiment, the
electrical resistance of the layer is about 0.001 ohms
per square inch for a 0.050 inch thickness.
The above mentioned separator material can be used
in a lead-acid battery. The battery includes a con
tainer, a plurality of electrodes substantially enclosed
by the container, and an electrolyte in substantial phy-
sical contact with the plurality of electrodes. A sepa-
rator material of this invention is placed in physical
contact with and substantially envelopes at least one
of the electrodes. It should be understood that various
dimensions and types of containers as well as electrodes
are contemplated for use in the present invention.
~0 ~igure 1 shows a perspective view of a battery having
a plurality of positive electrodes 30 and negative elec-
trodes 31 substantially enclosed by a container 32.
s parator material 34 is positioned between the positive
and negative electrodes. It is preferred, although not
necessaxy, for the separator material to be in substan-
tial contact with the whole face of the electrode. The
plate dimension or number of plates is not intended to
be limit2d.
~igure 1 also illustrates a preferred embodiment of
the invention. All of the negative electrodes 31 are
placed in substantial physical contact with the separator
material 34. However, it should be understood that the
present invention contemplates the use of ~he separator
material in substantial contact with any combination of
positive or negative electrodes.
1 15~3~3
-13-
A more preferred embodiment contemplates a separator
which covers bo~h sides and the bottom of all the negative
electrodes 31 with the separator material 34. This is
shown in Figure 1 at point 38. Any conven~ional means
may be used to envelope the separator material about ~he
electrode. It should be understood that the present in~
vention is not intended to be limited to any particular
style of envelope or wrap placing the separator material
in contact with the electrode. For example r a continuous
wrap may be used or separate shee~s o ~he separator ma-
terial may be sealed by any conventional means creating
an envelope configuration.
A battery having the separator material may also use
an electrolyte of the present invention. As stated else-
where in the specifications, ~he electrolyte would be insubstantial contact with the plurality of electrodes.
A method included in the present invention for making
a lead-acid battery having electrodes disposed in a COIl-
tainer includes filling the electrolyte space of the bat-
tery with the novel electrolyte of the present invention.Subsequently, the battery may be substantially sealed and
the electrodes of the battery are formed. Typical formation
processes will be discussed later in the specification. It
Chould be understood that the battery may be formed before
it is sealed. A major objec~ of the present invention is
not to have to remove-and replace the electrolyte afte,r
the foxmation process. The sequence and number of steps
following the filling of the electrolyte space is not
intended to be limited.
Another method of making a lead-ac.id battery having
electrodes disposed in a container includes the step of
enveloping an electrode of the battery with the novel
separator material of ~he present invention. The separator
material has ~he same characteristics as discussed else-
where in the specification.
~ 15~303
-14-
Having described the invention in general terms,
the following examples are set forth to more fully
illustrate the preferred embodiments of the invention.
These examples, however, are not meant to be limiting.
It is possible to produce still other embodiments
without departing from the inventive concept herein
disclosed. Such embodiments are within the abi~ity
of one skilled in the art.
Example 1
The characteristics of gel containing various
amounts of silica, alkali~ and sulfuric acid were
studied by mixing in laboratory beakers different
volumes of sulfuric acid having the specific gravity
of 1.400 and Ludox (S~-30). Ludox (5M~30) is manu-
factured by E. I. duPont de Nemours & Company. Typical
properties of Ludox tSM-30) are:
Stabilizing counter ion Sodium
Particle charge Negative
Av. particle diameter, nm 7
Specific surface area, m2/g . 360
Silica (as SiO2), wt ~ 30
pH (25C, 77F) 9-9
Titratable alkali (as Na2O), wt ~ 0.56
SiO2/Na2O (by wt) 54
Chlorides (as NaCl), wt % 0.01
Sulfates (as Na2SO4)' wt ~ 0.03
Viscosity (25C, 77F), cP, mPa-s 6
Wt. per gallon (25C, 77F), lb 10~0
Specific gravity ~25C, 77~) 1.22
A total of 10 mixtures were prepared and the se~ting
times needed for a gel to form out of liquid mix-
tures are recorded ln Figure 2. As indicated in the
figure, the gels with a setting time which is con-
venient to use have a silica content of about 1 to 7by weight.
~583~3
The gels were subjected to a penetration test to
measure their relati~e hardness. Samples of the gels
were placed in beakers. A hydrometer float 5 inches
in length, 5/8 inches in diameter and weighing 8 grams
was attached to the end of a shaft weighing 36 grams.
The shaft was suspended in a position where the float
met its image at the surface of the gel. The shaft
and float were r~leased and allowed to penetrate the
gel~ The measurements of ~he penetration are shown
in Figure 3. A preferred range of embodiments which
display the desired characteristics discussed pre-
viously have a silica content between about 3 to 4
by weigh~.
~hree groups of cells were formed with the 15
mixtures of sulfuric acid and Ludox SM-30 having an
acid/Ludox ratio of 6:1 through 20:10 The first five
mixtures were not selected becau_e of their high ~ard-
ness values as indicated by Figure 3.
The first group of cells consisted of 15 cells,
each having a different acid/Ludox ratio. The cells
included ~ive positive and negative plates constructed
with lead-4.5% antimony grids. The dimensions of the
plates were approximately 3 inches in length, 2.5
inches in width and 0.27 inches in depth. Fox each of
the cells, the total rated capacity was 12 ampere-hours.
The positive and negative plates were separated by
S-shaped spacers which were made out of mlcroporous
rubber material. These spacers were inert to the elec-
trolyte and their purpose was simply to prevent the
electrodes from touching each other. The negative
pla~es were wrapped with a material called Dexiglas
Mat, Grade X-42~5. This material i5 manufactured by
the C. H. Dexter Company and is a binderless, glass
microfiber mat of 100% glass composition. Fiber dia-
meter ranges from less than one micron to severalmicrons. Typical properties of this ma~erial are:
~ 1 S~3~3
-16-
Thickness: 0.050"
Softening Point: 1254F
Pore Size: 1 micron
(by bubble method)
Glass Composition: All "C" grade
Air Permability: 8.5 LPM per 100 CM
at a pressure differential
of 12.7 mm of ~ 0. (.050"
th.) 2
Tensile Strength: Dry, 1500 grams per 25 mm
width in machine directionO
Tensile strength, drv, is
950 grams in cross machin~
direction. ~.050" th.)
Electrical Resistance: 0.001 Ohms per inch for
0.050 inch thickness.
Material Weight: 170 grams per meter
(.050" th.~
Solubility: In boiling 1 normal sul-
furic acid for a period
of 1 hour is 9% - (pri-
marily sodium).
The second group of cells included one cell for
each of the 15 acid/Ludox ratios. The cells were of
~he same construction as the first group of cells
except that the neqative plates were not wrapped with
any material.
The third group of cells included six cells of the
same construction as the first group of cells except
that the positive and negative plates were separated by
means of conventional microporous separator material.
; Thus, spacers were not used to separate the positive
and neyative plates. Also, instead of a gel electro-
lyte of the present invention, conventional liquid
sulfuric acid having a specific gravity of 1.250 was
used as electrolyte. The performance of the conven
tional cells is representative of both liquid and
gel electrolytes in the prior art and the cells serve
as a control group.
~ ~ 5~3~3
A11 three groups of cells underwent the following
formation process. The cells were subjected to 120
hours of forma~ion split between two stages of 0.4
amps for 4 hours followin~ by 0.8 amps for 116 hours.
Following the completion of the formation process, it
was found that only the Eirst four compositions repre-
senting an acid/Ludox volume of 6:1 through 9:1 retained
their gel-like consistency.
The three groups of cells were dischar~ed at the
6 hour rate to determine their capacities. The results
of these tests are given in Figure 4. Unexpectedly,
the two groups of gel cells of the present invention
(with and without Dexiglas Mat) gave capaci~ies equal
to or higher than the group of conventional cells.
The gel cells with the Dexiglas material gave ~he high-
est capacity overall.
Figure 5 demonstrate~ the cell voltages and positive
potentials of the three groups of cells. Clearly, and
unexpectedly, the gel cell with the Dexiglas material
had higher cell voltages and pssitive potentials than
the other two groups of cells.
Figure 6 depicts the negative electrode potentials
for the three groups of cells. Once again, the gel
cells unexpectedly performed as well as the conventional
cells. The gel cells had a slightly lower negative
electrode potential than the conventional cells but,
totally within acceptable standards. These potentials
were measured against a cadmium/cadmium sulfate elec-
trode.
EXAm~
Four cells were constructed with lead-4.5~ anti-
mony grids for both the positive and negative plates.
The dimensions of the plates were approximately 16
inches in length, 5.5 inches in width and 0.25 inches
3s in depth. For each of the cells, conven~ional
~L ~5~3~3
~18--
mi-croporous separator material wrapped the plates and
the total rated capacity was 320 ampere-hours. The
cells were then placed in liquid sulfuric: acid elec-
trolyte having a specific gravity of 1.300. All of the
cells were then subjec~ed to 120 hours of formation split
between two stages of 0.4 amps fox 4 hours followed by
0. 8 amps for 116 hours. Following the ~ormation process,
the cells were cycled by discharging them to 100% depth
of discharge at the 6-hour rate and charging them back
with 110% of the output charge. An hour rate is defined
as the ~ime period in which the cell is totally discharged.
Therefore, a higher hour rate will allow one to discharge
a cell b~ draining less amperes over a longer time period.
Following these capacity buildup cycles, the separator
wrap in two of the cells were removed. Substituted in
place of the separators were small pieces of microporous
rubber spacers disposed between the positive and negative
plates. These spacers ~ere inert to the electrolyte and
their purpose was simply to prevent the electrodes from
touching each other. A gel electrolyte of the present
invention was ~hen placed in these two cells.
The gel elec~rolyte was prepared by mixing together
one part by volume Ludox SM-30 with three parts by volume
of sulfuric acid having a specific gravity of 1.400.
The two cells having the conventional separators
used in formation were placed in fresh liquid sul~uric
acid having a specific gravity of 1,300. This set of
conventional cells represented cells of the prior art
and served as a con~rol set. Different ~ests were then
performed upon both sets of cells.
The capacity performances of the two sets of cells
are shown in Figure 7. Both the conventional cells and
the gel cells of the present invention exhibit comparable
discharge capacity at various rates of discharge. These
discharge rates are the time periods in whi~h the cells
were discharged 100~.
3 ~ 3
--19--
Figure 6 reflects the percentage of xated capa-
city at the 6-hour rate of discharge against the number
of cycles. Unexpectedly, the gel cells c~f the presen~
invention performed as well as the conventional cells.
Figure 9 shows the percentage of rated capacity
at the l-hour rate of discharge against the number of
cycles. Once again, the gel cells of the present in-
vention had similar performance to the conventional
cells.
Figure 10 shows the gas evolution characteristics
of the conventional cells and the gel cells of ~he
present invention after being subjec~ed to different
percentages of chargeback. The chargeback i5 based on
the charge taken out during capacity discharge prior to
the chargeback. The figure shows that with 110~ of
chargeback, a conventional cell produced a total of 0.8
cubic feet of gas. Unexpectedly, with the same amount
of chargeback, the total volume of ~he accumulated gas
produced by a gel cell was less than 0.05 cubic feet.
These dramatic results demons ~ate that a gel cell of
the present invention produces over 16 times less gas
than the comparable prior art cell. Even wi~h a charge
back of 135%, the total gas evolved in a gel cell of
the present invention was less than 0.2 cubic feet.
Therefore, even with considerably more chargeback, a
gel cell of the present inven~ion clearly has superior
performance over prior art cells.
Figure ll shows the results of the rate of gas
evolution by ~he two sets of cells over an extended
period of overcharge. During the continuous over~
charge period of 30 days, the rate of gas evolution
of the conventional cells remains constant at approx-
imately 0.024 cubic feet per ampere hour. Wholly
unexpectedly, a gel cell of the presen~ invention has
3~ a rate of gas evolution of approximately 0.006 cubic
feet per ampere hour. Even more dramatically, this
3 ~
-20-
rate was decreasing duri~g the overcharge, eventually
becoming negligible at the end of the thirty day period.
Therefore, the problem of gassing in a maintenance free,
sealed cell would be eliminated by a cell encompassing
the present invention.
Example 3
Three cells were constructed with lead-4.5% anti-
mony grids for both the positive and negative plates.
The dimensions of the plates were approximately 15
inches in length, 5.5 inches in width, and 0.25 inches
in depth. For each of ~he cells, the to~al rated capa-
city was 450 ampere-hours. The negative plates of the
cells were wrapped with Dexiglas material and the posi-
tive and negative plates were separated by S-shaped
spacers. The three cells were respectively filled with
4:1, 5:1, and 6:1 volume mixtures of sulfuric acid
having the specific gravi~y of 1.400 and Ludox SM 30
which respectively ga~e the silicon dioxide content
of 5.4%, 4.5% and 3.8%.
A conventional cell was constructed having the
same design as those above except that a conventional
microporous separator material was substituted in
place of the Dexiglas material, S-shaped spacers were
not used between the positive and negative plates and
conventional liquid sulfuric acid having a specific
gravit~ of 1.250 was used as the electrolyte. This
conventional cell representad cells of the prior art
served as control.
The four cells underwen~ the formation process
described in Example 1. Subse~uent to the formation
process, the four cells were subjected to four cycles
of discharge at the 6-hour rate following by 110
chargeback.
Figure 12 depicts the capacities of the cells
after the four discharges. Unexpectedl.y, and quite
dramatically, the gel cells of the present invention
~ ~5~33~33
-21
allevia~ed the problems associated with formation of
the b~ttery af~er is has been assembled~ The gel
electrolyte can now be used in situ, thereby eliminating
the time and expense involved with changing electrolyte
after the formation process.
Ex~ple 4
Two groups of cells were constructed having the
same pla~e dimensions and number of plates as in Example
1~ The first groups of cells separated ~he positive and
negative plates by using S-shaped spacers made out of
microporous rubber material. The second group of cells
had the negative plates wrapped with Dexiglas Mat and
once again separated the positive and negative plates
with S-shaped spacers of the same rubber material.
Both groups of cells were subsequently filled with
gel electrolyte. The gel used for both groups of cells
was prepared by mixing sulfuric acid having a specific
gravity of 1.400 and ~udox (SM-30) and in the acid/Ludox
ratio of 6:1 by volum~.
A formation period then followed the filling of the
cells. The following procedure was used to form the
cells. Approximately 120 hours of formation were ~plit
between two stages of 0.4 amps for 4 hours followed by
0.8 amps for 116 hours.
Following the formation period, the cells were
cycled by discharging them to 100% depth of discharge
at an 6-hour rate and charging them back with 100% of
the output charge. ~igure 13 depicts the performance
by cycle of the ~w~ groups of cells. The capacity of
the group of cells used as ~he control dropped below
80% of their rated value after 17 cycles. Unexpectedly,
the group of cells using the Vexiglas wrap on the nega-
tive plates gave 84 cycles before their capacity dropped
, below 80~. The cells of ~he presen~ invention utilizing
the Dexiglas wrap show a drama~ic improvement in capaci~y
:~ 15~3~3
-22-
of approximately 500% over the cells without Dexiglas~
Fi~ure 14 shows the cell voltage of t:he two groups
of cells at the end of chargeback. The group of cells
without Dexiglas indicated a continuou~ decrease in the
cell voltage early in the period o~ cycling. By the end
of cycle 22, their capacity was less than 20% of the
rated Yalue. The voltage of the cell a~ the end of
chargeback had lowered to a value of 2~ 25 volts from
the initial value of 2.38 volts recorded af~er the first
cycle. The cells with Dexiglas had a voltage at the end
of chargeback of 2.52 even after 100 cycles.
The positive electrode potentials for the two groups
of cells arP depicted in Figure 15. These potentials
were measured with a Cd/CdSO4 electrode. The negative
electrode potentials of the two groups of cells at the
end of chargeback during cycling are given in Figure 16.
These negative potentials were measured with the same
elec~rode used in Figure 4. The group of cells using
the Dexiglas showed a surprisingly high resistance to
degradation of the negative electrode as compared to
the group of cells without Dexiglas.
Figure 17 reflects the positive electrode potential
at the end of discharge of the two groups of cells after
different periods of cycling. The cell voltage was 1.70
volts during the period of cycling.
Figure 18 indicated the negative elec~rode potential
at the end of discharge of the two groups of cells during
the period of cycling represented by Figure 17. Once
again~ the negative electrode showed surprisingly little
degradation.
As demonstrated by these examples, this invention
provides a gel electrolyte which eliminates the need for
canstant main~enance during the life of the battery and
the possibili~y of spilling the electrolyte from the
battery. The gel electrolyte not only reduced gassing
of the battery electrodes during cycling but also improves
3~3
-23-
the cycle life and capacity of the bat ery compared
to prior art cells. Additionally, the gel electrolyte
serves as a separator between the electrodes o a ba~-
tery, therefore, eliminating the need or separator
material to be used.
This invention provides an economical electrolyte
which can be used in situ for both the formation of
battery electrodes as well as later cycling of the
battery service. The electrolytes of this invPntion
eliminate the additional time and expense caused by
the need to change electrolyte after use in the for-
mation process.
This invention also provides a separator material
which is easily and conveniently disposed in contac~
with the electrodes of a battery. As demonstrated
throughout the specification, the separator material
of the present invention improves the capacity and the
cycle life of a battery compared to prior art cells.
Al~hough the invention has been described and
illustrated in detail, it is to be clearly understood
that the same is by way of illustra~ion and example
only and not to be taken by way of limitation, the
spirit and scop~ of this invention being limited
only by the terms of the appended claims.
