Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to a lead salt electric storage
battery with electrodes of first order, i.e. a battery in which
the active materials are deposited as coatings on the electrodes
during charging and are again dissolved in the electrolyte during
discharging. Such batteries are known per se.
Electric batteries with electrodes of first order and
electrolytes other than lead salts are also known in a great many
varieties, and many of these have satisfactory properties for
various uses. However, the invention is directed specifically to
the problems of lead salt batteries, which have the potential
advantage of providing a relatively inexpensive medium for the
reversible storage of electric energy for general purposes.
Lead salt electric storage batteries of the type con-
sidered are known from the Western German published applications
Nos. 2,451,017 and 2,532,512. These batteries contain as
electrolyte aqueous solutions of lead salts of perchloric acid,
tetrafluoro boric acid, hexafluoro silicic acid and/or amido
sulfonic acid. From the electrolyte lead dioxide and metallic
lead are deposited during charging on the anode and the cathode
respectively in the form of coatings, from which they are again
dissolved during discharging. By the anode is to be understood,
throughout this specification, the electrode which forms the
positive pole during discharge. In the known batteries con-
sidered bhe anode consists of a porous, graphite-filled artificial
resin having a pore volume of 20-70% and containing 50-80%
graphite by weight.
It is the object of the invention to construct a lead
salt electric battery with electrodes of first order and with an
anode body comprising graphite in such a manner as completely to
avoid the development of gas, even transitionally, within the
cell or each cell of the battery, while at the same time obtaining
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compactness of structure, a high mechanical, electrical and
chemical stability and a high amp-hours capacity in relation to
volume and weight.
According to the invention, there is provided lead salt
electric storage battery with electrodes of first order, having
an active anode body comprising graphite, the combination
comprising:
a) the active anode body comprising a textile material
graphitized at a temperature of at least 2500C;
b) the active anode body is connected with an electro-
lyte-impervious. electrically conductive cell closure comprising
molded artificial resin with molded-in, uniformly distributed
short-cut graphite fibers graphitized at a temperature of at
least 2500C;
c) the connection between the active anode body and the
cell closure is established through a uniting interface layer
consisting of artificial resin with graphite fibers embedded
therein, said graphite fibers being graphitized at a temperature
of at least 25Q0C;
d) the electrolyte comprising a mixture of lead silico-
fluoride and lead methane sulfonate dissolved in water, the pro- .
portion of lead silicofluoride ranging from 100 to 0%.
It has been found that with the above mentioned combina-
*ion:ilof construction materials and electrolyte, development of
gas in the cell is comple~ely avoided, and a high chemical
stability is achieved. An important factor in achieving this
result is that the only electrically conducting material, to
which the electrolyte has access on the anode side of the cell,
is graphite which has been graphitized at a temperature of at
30 least 2500 C.
A graphitized textile material distinguishes itself by
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having a great pore volume, e.g. about 85%, and the textile
structure provides a particularly great pore surface as related
to the pore volume. This surface consists of pure carbon in
graphite form as contrasted to the combined carbon and artificial
resin surface of the anode in the known lead salt batteries
referred to above. This contributes to obtaining a high amp-
hours capacity for a given volume and a given weight of a battery
cell. In spite of the great pore volume a graphitized textile
material has a satisfactory mechanical strength. Graphitized
textile materials are available on the market and are e.g. used
as a reinforcement for artificial resins. An example of a
graphitized textile material is the product sold under the trade
mark SIGRATEX by Sigri Elektrographit GmbH. It is available in
different types indicated by the addition of numerals indicating
the woven structure and the graphitizing temperature which varies
from 1000C to 2600C. As mentioned, for the purposes of the
present invention, a material graphitized at a temperature of at
least 2500C should be used. A material marketed under the
denomination SIGRATEX GDS 8-30 has been used for the construction
of batteries according to the invention with good results. This
material has been made by graphitizing a textile material consist-
ing of polyacrylonitrile. It may be possible to develop other
graphitized textile materials specially adapted for use as an
anode material provided that the critical
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minimum graphitizing temperature of 2500C is observed. Advantageously,
the pore volume of the graphitized textile material amounts to about
40-70% of the total electrolyte volume. The anode body may, if necessa-
ry, consist of more than one layer of the graphitized textile material.
5 E.g. the above mentioned commercial product is available in a layer
thickness of 0. 9 mm and when using this material it has been found
suitable to employ more than one, e.g. three layers of this material in a
battery according to the invention. When two or more layers of
graphitized textile material are used, these may suitably be connected
10 with each other by sewing, preferably with graphite yarn. Thereby a
very intimate electrical connection is obtained between the various
layers of graphitized textile material. As a further possibility a plurality
of textile material layers may be stitched together before the
graphitizing so that the sewing yarn is graphitized together with the
15 layers, or by special weaving methods a material may be produced
which consists of a plurality of inter-woven layers which are then
graphitized as a whole. It may also be possible to use a pile fabric.
When a plurality of layers of graphitized textile material is
used, an alternative method of interconnecting these is to glue them
20 together spot-wise by means of an electrically conducting glue or adhesi-
ve which should then fulfil the same conditions as will be specified
below for the gluing together of the anode body and the cell closure
This is a simple method, but it will result in some reduction of the
capacity and some increase of the contact resistance between the various
25 layers.
Examples of artificial resins suitable for the moulding of the
cell closure are polyethylene, polypropylene or polystyrene, with which
graphite fibers are admixed before the moulding. Other artificial resins
may also be used, provided of course that these materials do not in
30 themselves give rise to the development of gas under the conditions
prevailing in the cell, which may easily be determined by experiment
The graphite fibers are referred to above as "short-cut", and one way
of producing such graphite fibers is to crush a graphitized textile
material, such as that used for the anode body. It is advantageous,
35 however, that the particles thereby produced should still have an
elongated fibrous shape, because this contributes to increasing the
conductivity of the cell closure. The graphite content may e.g. amount
to about 30%.
For the purposes of the invention it is not essential that the
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element referred to as cell closure should in itself have a sufficient me-
chanical strength for structural purposes. Its function is to close the
cell chemically on the anode side and it could fulfil this function even if
it were in the form of an electrolyte-impervious film or coating on a
plate of higher mechanical strength.
Examples of artificial resin glues or adhesives suitable for
connecting the active anode body with the cell closure are polyisobutyle-
ne solution and polystyrene solution, with which graphite fibers are
admixed as above mentioned. Other artificial resins may also be used,
provided that they have satisfactory adhesive properties and do not in
themselves give rise to the development of gas under the conditions
prevailing in the cell. The gluing may take place over the whole area of
the anode, but it is important that the glue does not to a substantial
extent penetrate into the graphitized textile material because the pore
volume would thereby be reduced. As regards the graphite fibers to be
admixed with the glue, the same conditions apply as to the graphite
fibers of the cell closure.
I n the alternative method of uniting the anode body and the
cell closure by embedding fibers at the surface of the active anode
body in the artificial resin of the cell closure, the temporary softening
of the surFace of the said artificial resin may be performed by applying
a volatile solvent, such as chloroform, to the surface of the cell closure,
whereby the artificial resin material of the cell closure is superficially
dissolved, whereafter the anode body is pressed against the cell closure,
e.g. by weight-loading, so that the textile fibers at the surface of the
anode body may penetrate into the softened artificial resin. When the
solvent has evaporated, the artificial resin again becomes solid and
thereby firmly holds the fibers of the textile materiale, while at the
same time an ideal electric connection is established between the fibers
of the anode body and the graphite fibers in the artificial resin material.
An alternative method which has substantially the same result is to weld
the anode body to the graphite-containing artificial resin material under
the application of heat which wholly or partly melts or fuses the surface
of the artificial resin material.
The use of lead silicofluoride (PbSiF6) as an electrolyte is
known per se, but not in combination with the structural arrangement
of a cell as above described. As mentioned, lead methane sulfonate
(Pb(CH35O3)2) may be used as an alternative to lead silicofluoride,
though the capacity will thereby be somewhat reduced. The best results
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are obtained by using a mixture of lead silicofluoride and lead methane
sulfonate in water. By adding lead methane sulfonate to lead silico-
fluoride an increase of the conductivity of the electrolyte is observed,
and it is assumed that additionally a dissociation of a greater number of
5 double negative lead salt ions is obtained. The advantage obtained by
the use of lead methane sulfonate occurs already at a relative low
proportion of this material and increases with this proportion up to a
certain limit. According to the tests that have been run optimum results
are obtained by using an aqueous solution which is about 1 . 8 molar in
10 respect of lead silicofluoride and about 1.2 molar in respect of lead
methane sulfonate. Moreover, the electrolyte may advantageously contain
a small excess, about 0.15 molar, of the corresponding acids.
In the known lead salt batteries with electrodes of first order
it is customary to arrange the electrodes in vertical position and to cir-
15 culate the electrolyte along the electrodes by means of special pumpingdevices. These increase the weight of the battery, consume energy and
detract from the reliability of the battery, because they are vulnerable
and complicated devices . I n contradistinction thereto, in accordance
with a preferred embodiment of the invention, the cell or each cell of
20 the battery is permanently hermetically closed - and, at least during
charging, is disposed with the electrodes in horizontal position and with
the anode at the top. This arrangement is possible because the develop-
ment of gas in the battery cell has- been completely avoided, and owing
to the horizontal arrangement of the electrodes the necessary movement
25 of the electrolyte may take place by diffusion so that no pumping is
required. By placing the cathode at the bottom of the cell during
charging, the danger of the formation of dendrites with consequent
danger of short-circuit is prevented.
The hermetically closed cells can be filled with the electrolyte
30 by injection through a hole which is then closed by a stopper. If neces-
sary, each individual cell may be provided with an expansion chamber
or an expansible wall. Where a number of cells are surrounded by a
common wall, this may e.g. be constructed in the form of a bellows.
The material or materials used for the cathode, on which
35 metallic lead is deposited during charging of the battery, are not subject
to any critical conditions. For reasons of economic production it may be
practical to make the cathode from the same materials as the cell closure
on the anode side. This is particularly the case where a number of cells
are superposed to form a multi-cell battery, because the anode may
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then simply be used as a bipolar electrode, the cell closure part of the
anode forming the cathode of the cell next above. A cathode exactly
corresponding to the cell closure of the anode, but without any anode
body attached thereto may then form the bottom of the stack, and since
5 this, like the cell closure, is electrically conducting, external conductors
may be directly connected to these elements. Various examples of the
connection of external conductors to the end elements of a battery will
be described in the following.
The invention will now be described in further detail with re-
10 ference to some examples illustrated in the drawing, in which
Fig. 1 shows diagrammatically a section through a one-cell bat-
tery representing a first and a second example,
Fig. 2 shows a broken longitudinal section through a seven-
cell battery representing a third example,
Fig. 3 is a side view of a sixty-cell battery representing a
fourth example,
Fig. 4 shows on a larger scale a vertical part section through
the battery of Fig. 3, and
Fig. 5 is a top view of the battery of Fig. 3.
20 Example 1: One-cell battery, Fig. 1.
Two elements are made by moulding under heat and pressure
from a mixture of one part by weight of polyethylene and two parts by
weight of short-cut, e.g. crushed graphite fibers. The two elements,
which each constitutes a circular plate with a thickness of 0.4 mm and a
25 diameter of 50 mm with a protruding collar portion, are referred to as
anode cap 1 and cathode cap 2 respectively. The anode cap 1 is electro-
lytically copper-plated on its outer face to form a thin layer 3, while an
anode body 4 consisting of graphitized porous textile material is glued
to the inner face of the anode cap 1 over the whole of its area by
30 means of an electrically conducting glue S consisting of polyisobutylene
and short-cut graphite fibers. The porous textile material, which has
been graphitized at 2500C, has a thickness of 2.7 mm and a pore
volume of 85%. The cathode cap 2 is electrolytically copper-plated on its
outer face to form a layer 6. A piece of liquid-permeable polypropylene
35 paper 8 is glued to a thin-walled polyvinylchloride ring 7 so as to
extend smoothly and in a stretched state across the cross-sectional area
of the ring 7. The anode cap 1 is introduced into the ring 7 on one
side of the polypropylene paper 8 so as to bring the graphitized porous
textile material 4 into contact with the polypropylene paper 8, whereafter
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the cap 1 is -Fixed to the ring 7 by gluing. On the other side of the
polypropylene paper the cathode cap 2 is introduced into the ring 7 and
fixed by gluing in a position such that the free distance from the
polypropylene paper 8 to the cap 2 is 2 mm. The polypropylene paper
serves as a liquid-pervious supporting diaphragm or separator which
prevents any detached graphite particles from penetrating into the
electrolyte .
A hole is bored in the side of the ring 7, the electrolyte is
injected and the hole is closed by means of a silicon rubber stopper.
The electrolyte is an aqueous solution which is 3-molar in respect of
lead silicofluoride and which additionally contains a small excess, 0.15-
molar, of the corresponding acid.
With such a cell the following test results have been obtained:
By charging with 0.5 A the cell takes up 0.69 Ah. By dis-
charging with 0.35 A it delivers 0.65 Ah in the course of 112 minutes,
while at the same time the pole voltage drops from 1.8 V to 1.4 V. The
average voltage during discharge is 1.66 V and the specific energy con-
tent is 46 Wh/kg.
Example 2: One-cell battery, Fig. 1.
The build-up is the same as in example 1, however, the elec-
trolyte is in this case an aqueous solution which is 1.8-molar in respect
of lead silicofluoride and 1.2-molar in respect of lead methane sulfonate.
Moreover, there is a small excess of the corresponding acids corre-
sponding to 0.15-molar.
The following test results have been obtained:
By charging with 0.5 A the cell takes up 0.69 Ah. By dis-
charging with 0.35 A it delivers 0.65 Ah in the course of 112 minutes,
while at the same time the pole voltage drops from 1.8 V to 1.4 V . The
average voltage during discharge is 1.69 V and the specific energy con-
tent is 49 Wh/kg.
Example 3: Seven-cell battery, Fig. 2.
Six identical caps 11 are made by moulding under heat and
pressure from 11 parts by weight of polystyrene and 10 parts by weight
of crushed graphite fibers. The caps have a thickness of 0.5 mm and a
diameter of 150 mm and are constructed with a protruding collar portion.
Moreover, a top cap 12 and a bottom cap 13 are produced, each having
a thickness of 1 mm. Tin-plated steel plates 14 and 15, respectively,
having a thickness of 0.25 mm, and to which tin-plated steel wire
nets 16 and 17, respectively, are attached by spot soldering, are
pressed into the top cap 12 and the bottom cap 13, respectively. An
anode body 19 having a thickness of 2.7 mm and consisting of porous
textile materiai graphitized at 2500C and having a pore volume of 85%
is fixed to each of the caps 11 and 12 in an interface layer 18 by means
5 of chloroform vapour. The caps are introduced into and glued to a
thin-walled polyvinylchloride tube 20 in the following succession starting
from the bottom: 13, 11, .. , 11, 12. Immediately below each anode
body 19 a piece of liquid-permeable polypropylene paper 21 is mounted
at a distance of 2 mm from the cap 13, 11, .. , 11 next below by
10 means of 2 mm high spacing rings distributed over the cross-sectional
area .
Electrolyte is injected through holes bored in the wall of the
tube 20, and the holes are then closed by means of silicon rubber stop-
pers . The electrolyte is an aqueous solution which is 1.8-molar in
15 respect of lead silicofluoride and 1.2-molar in respect of lead methane
sulfonate. Moreover, there is a small excess, 0.15-molar, of the corre-
sponding acids.
The following test results have been obtained:
By charging with 4.5 A the battery takes up 6.2 Ah. By
20 discharging with 3.15 A it delivers 5.8 Ah in the course of 110 minutes,
while at the same time the pole voltage drops from 12.6 V to 9.8 V.
The average voltage during discharge is 11.8 V and the specific energy
content is 50 Wh/kg.
Example-4: Sixty-cell battery, Figs. 3, 4 and 5.
Fiftynine identical caps 41 are made by moulding under heat
and pressure from 11 parts by weight of polystyrene and 10 parts by
weight of crushed graphite fibers . The caps have a thickness of 0.5
mm, are square with a side length of 550 mm and are constructed with
a protruding collar portion. A top cap 42 is made from the same polysty-
30 rene/graphite fiber mixture and has a thickness of 1.5 mm . Moreover,
an aluminum top cover 43 is made by injection moulding in the form of a
square plate which on its upper side is constructed with re-inforcement
ribs 53 and an upwardly extending edge 54. A circular plug 52 of steel
is pressed into a hole of the top cover 43 by crimping. The plug 52 is
35 tin-plated on its top face. It serves for the connection of an outer
supply conductor by means of a magnet. The aluminum top cover 43 is
tin-plated on its underside, and a tin-plated steel wire net 44 is attached
thereto by a multitude of spot solderings. The aluminum top cover is
pressed into the top cap 42 with application of heat.
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A bottom cap 45 having a thickness of 1.5 mm is made from
the same polystyrene/graphite fiber mixture. A bottom cover 46 consist-
ing of a steel plate, which is provided with a collar 55 and a flange 56,
fits in the bottom cap. The flange 56 extends beyond the contour of the
5 bottom cap and is provided with holes 47 for the electrically conducting
fastening o-f the battery. The steel plate is tin-plated on its upper face
and a tin-plated steel wire net is attached thereto by a multitude of
spot solderings. The bottom cover 46 is pressed into the bottom cap 45
with the application of heat. An anode body 48 having a thickness of
3.6 mm and consisting of a porous textile material graphiti~ed at 2500C
and having a pore volume of 85% is welded into each of the fiftynine
caps 41 by means of chloro-form vapour. The caps are introduced into a
square polyvinylchloride tube 49 and glued thereto in the following
succession counted from the bottom: 45, 41, .. , 41, 42. Imme-
15 diately below each anode body 48 a piece of liquid-permeable polypropy-
lene paper 50 is mounted at a distance of 3.3 mm from the cap 45, 41,.
...., 41 next below by means of small spacing rings (not shown) distri-
buted over the cross-sectional area and having a height of 3.3 mm .
The electrolyte is injected through a hole bored for each cell
in the wall of the tube 49, whereafter the holes are closed by means of
silicon rubber stoppers. The electrolyte is an aqueous solution which is
2-molar in respect of lead silicofluoride and 1-molar in respect of lead
methane sulfonate. Moreover, there is a small excess of the correspond-
ing acids corresponding to 0.15-molar.
For this ba-ttery the following values have been calculated:
By charging with 70 A the battery takes up 136 Ah. By
discharging with 62.5 A it delivers 125 Ah in the course of 120 minutes,
while at the same time the pole voltage drops from 110 V to 84 V. The
average voltage during discharge is 102.5 V and the specific energy
content is 52 Wh/kg.
The term "artificial resins" as used in the description and
claims of this application should be interpreted in its broadest sense,
i.e. as generally synonymous with "plastics materials" (in German
" Kunststoffe" ) .
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