Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to an electric storage battery.
Alkaline accumulators and lead-acid batteries are most
important power sources since a long time ago. Both have
advantageq and disadvantages and the two battery types cannot be
said to compete on the market.
The alkaline accumulators are much more expensive to
manufacture than the corresponding lead-acid batteries since the
positive electrodes contain expensive electrode materials,
frequently nickel oxide, but sometimes also silver oxide. The
today dominating embodiment of alkaline accumulators d oe s further-
more u~e cadmium as negative electrode material, which is
expen~ive and poi~onous. Iron has therefore recently attracted
attention as negative electrode material in alkaline accumulators.
The lead-acid battery has a bigger market than the
alkaline accumulators depending on lower cost and satisfactory
performance and life for many applications including traction
applications. The lead-acid battery, however, use~ heavy
electrode and conqtruction materials. The electrolyte in the
lead-acid battery, most frequently sulphuric acid, is also
consumed in the cell reaction contrary to the case with
alkaline accumulators, where the composition of the electrolyte
in general does not change during charge and discharge. The
theoretically possible energy density for the acid-lead battery
is therefore low.
Several new applications put up special requirements
on the batteries, for instance traction applications like
electric cars and stationary applications like load levelling
batteries for power systems. Common features for these new
applications are the demands on very low manufacturing costs,
high efficiency in the energy conversion, simple design, no
maintenance requirements, long life etc. In the traction
application a high power and energy density is furthermore
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desired, which is a less pronounced requirement in the case of
load levelling batteries for power grids, where first cost and
life and, of course, the conversion efficiency are most important
factors. There is, therefore, a need for a battery which com-
bines the good properties of the lead-acid batteries and the
alkaline accumulators. The present invention is concerned
with such a new electric battery from an electric storage
battery comprising at least one electrochemical cell having a
positive electrode, a negative electrode, and an electrolyte,
the active material of said negative electrode in its charged
condition being a member of the group consisting of iron,
cadmium, magne~ium, indium, and zinc, the active material
of said positive electrode in its charged condition comprising
lead dioxide or a difficultly soluble tetravalent lead compound
formed by the reaction of lead dioxide and the anion in the
electrolyte, qaid electrolyte comprising an alkaline-reacting
aqueous solution containing an alkali hydroxide in sufficient
amount to impart an alkaline reaction during the complete
electrochemical cycle and a 9alt who~e anion forms a difficultly
~oluble compound with the positive electrode material at least
in its discharged condition.
Thi invention represents namely a new physical
combination of components from the alkaline batterie~ and
components from the lead-acid battery, which is completely
unexpected for the expert. The battery according to the
invention utilizes namely the positive electrode of the lead-
acid battery and a negative electrode taken from the alkaline
accumulator, preferably an iron electrode, and an electrolyte
which may be a mixture of the electrolyte of the alkaline
accumulator and the electrolyte of the lead-acid battery, i.e.,
a water solution of an alkali sulphate and an alkali hydroxide.
The invention thus refers to a rechargeable chemo-electric cell
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or an electric accumulator comprising such cells containing a
positive electrode, an ion conducting electrolyte and a
negative electrode and other means required for the operation
of the cell in which the active material in the negative
electrode in its charged condition is iron, cadmium, magnesium,
indium, or zinc and that the active material in the positive
electrode in its charged condition is lead dioxide or other
difficultly soluble lead (IV) compounds which are formed
from lead dioxide and the anion in the electrolyte which is a
water Qolution containing alkali hydroxide with alkaline
reaction during the whole electrochemical cycle and a salt,
the anion of which forms a compound with that positive electrode
material at least in its discharged condition.
Thus according to the invention there is provided an
electric Atorage battery comprising at least one electrochemical
cell having a positive electrode, a negative electrode, and an
electrolyte comprising an alkaline-reacting aqueous solution con-
taining an alkali hydroxide in sufficient amount to import an
alkaline reaction during the complete electrochemical cycle and
a ~alt whose anion forms a difficultly soluble compound with
the positive electrode material at least in its discharged
condition, the active material of said negative electrode in its
charged condition being a member of the group consisting of
iron, cadmium, magnesium, indium and zinc, the active material
of said positive electrode in its charged condition comprising
lead dioxide or a difficultly soluble tetravalent lead compound
formed by the reaction of lead dioxide and the anion in the
electrolyte, the active material of said positive electrode in
its discharged condition comprising a difficultly soluble di-
valent lead compound formed by reaction of the electrode materialwith the anion in said electrolyte, said salt being present in
an amount sufficient to prevent the active material of the positive
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electrode in its charged and discharged condition from going
into solution.
In order that the invention be more readily under-
stood reference is made to the accompanying drawings in which:
FIGURE 1 iS a cross section through the case of one
embodiment of a storage battery according to the present
invention showing the internal structure:
FIGURE 2 is also a section through the case of a
aecond embodiment in accordance with the invention showing
the arrangement for a battery with bipolar electrodes,
FIGURE 3 is an enlarged schematic representation of
a portion of a battery having large bipolar electrodes for
load levelling batteries in accordance with the invention:
FIGURE 4 is a section through a "button-type"
battery made in accordance with the present invention, and
FIGURE 5 is a schematic representation of one system
for circulating the electrolyte through a bed of solid salt
to maintain a high concentration of anion.
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The invention will be exemplified in the following
with a particularly advantageous embodiment where the
negative electrode material iq iron, Fe, and the positive
material lead dioxide, ~-PbO2, and the elecrrolyte a water
solution of potassium hydroxide and potassium sulphate, for
instance 3.5 Normal KOH + 5% K2S04. The cell reactions during
discharge of this cell can be described in the following way:
At the anode:
I) 5Fe + 10 OH -~ 5Fe (OH)2 + 10 e
At the cathode:
II) 5Pb2 + 10 e + K2S04 + 7 H20 -~ Pbso4~4pbo.H2o + 2KOH +
10 OH
Adding the two reactions, there is obtained:
III) 5 Fe + 5PbO2 + K2S04 + 7 H20--~5 Fe (OH)2 + PbS04 4PbO.H20
+ 2KOH
It is also possible that the cell reactions follow
a different course. At a lower alkalinity tri-basic lead
sulphate may form inAtead of a tetra-basic lead sulphate etc.
The ~mportant thing from a practical point of view is that
the cell can take a load with current densities above about
5 mA/cm2. The cell voltage is in general within the range
1-2 V and depends on the state of charge, the composition
of the electrolyte and the current density.
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The cell can be charged thanks to the formation of electro-
chemically active salts with low solubility containing divalent
lead thanks to the salt addition to the electrolyte which prevents
the lead from going into solution as plumbite. Even if the re-
S action scheme is of a tentative character, it gives someinformation about the properties of the new power source. The
alkalinity of the conductivity of the electrolyte increases
during the discharge since water is consumed and sulphate ions
are shifted against hydroxyl ions. This provides for an effi-
cient use of the electrode materials. The volume changes ofthe systems are comparative small and therefor only moderate
volume additions are necessary to make up for these volume changes.
There is no difficulty for the expert to design and manu-
facture power sources of the new kind for different purposes
with the knowledge of the spirit of this invention. One is
thereby not restricted to the system which has been discussed
above, which, however, is particularly advantageous. Cadmium
may for instance be used instead of iron, where one may pre-
ferably use known sintered, alternatively so-called pressed
(with a plastic binder) electrodes, or so-called pocket
electrodes. Also zinc electrodes can be used in various known
embodiments, for instance with a catalytically active third
electrode to prevent short-circuits through dendrites, addition
of ions like Ca to form zincates with low solubility, etc.
The separator materials can be made of alkali resistant porous
materials, like cellulose, Cellophane~9 (a paper-like product
of viscose obtained by precipitation of viscose solution with
ammonium salts), nylon, polypropylene, rubber etc. With respect
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to anode materials and separators one may rely on the use
known technology for alkaline accumulators as described
in U. Falk and A. Salkind, "Alkaline Storage Batteries",
(John Wiley & Sons, Inc., 1969). Iron electrodes with
high capacity denAity can preferably be manufactured
according to the recipes in the Swedish patent 360,952.
The positive plate follows a somewhat different electro-
chemical scheme than the po3itive electrode of the conventional
lead-acid battery. It has, however, been found that
known po~itive lead dioxide electrodes can be used in
power sources according to the invention. An advantage is,
however, that current conductors, grids and other supporting
structure3 can be made in lighter and stronger materials,
like nickel-plated iron, thanks to the alkaline environment
in power sources according to the invention. The state of
art in this i9 well described for in~tance in C.V. Vinal,
"Storage Batteries", (John Wiley & Sons, Inc., 1967), or C.
Drot~chmann, "Bleiackumulatoren" (Verlag Chemie, 1951).
It i~ also known that formation in an alkaline environment
produce~ PbO2 with very good electrochemical and as well
other properties. Tri-basic and tetra-basic lead sulphate
are al~o known as very good electrode materials and are
sometimes used as starting materials for the manufacture
of po~itive electrodes for conventional lead batteries
with acid electrolyte. It is in this case particularly
advantageou~ to u~e as additive to the electrolyte-soluble
~ulphate9 like K2S04, Na2S04, Li2S04, etc. It is thereby
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preferable to use an excess of sulphate for instance in
the porous positive electrode, in which case the electrolyte
is saturated with sulphate. In this way it is also possible
to restrict the volume of the electrolyte and the sulphate
formation during discharge is accelerated and the voltage
stabilized. The sulphate concentration in the electrolyte
should preferably exceed 0.01 M and it is advantageous to
be above 0.1 M, preferably around 0.2-0.4 M. The alkalinity
increases during discharge and should preferably be within
the range 0.5-N to 12-N. An advantageous range is frequently
2-N to 8-N. The electrolyte may also contain additives of
other anions like carbonate, phosphate, silicate, zincate,
etc., whereby the corresponding difficultly soluble lead salts
or mixtures thereof are formed during discharge. Other known
additives like sulphides as alkali metal sulphides may also
be used.
It is evident from the above discussion that alkaline
batteries and lead-acid batteries of the state of art can
easily be converted to power sources according to the
invention by substitution of the positive or negative
electrodes and change of the electrolyte composition. The
alkaline environment gives great freedom with respect to
choice of design materials, makes possible simple design
of batteries with bipolar electrodes which is a difficult
problem with batteries with acid electrolyte.
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DESCRIPTION OF PREFERRED EMBODIMENTS
FIGURE 1 shows the principle design of a power source
containing three negative electrodes connected in parallel
(1) and two positive electrodes (2) connected in parallel.
The electrodes are separated by means of a separator (3)
and contained in the cell vessel (4) with the electrolyte
(5). The electrodes are connected with conductors (6)
respectively (7) which are connected to the pole bolts (8)
and (9) respectively which are situated in the cover (10)
of the cell vessel which contains an opening (11) with a
plug (12). The battery cell is thus built according to the
state of art for alkaline accumulators and lead batteries
but with positive and negative electrodes and electrolyte
according to the present invention.
The power source according to FIGURE 1 can be built up
completely with components that are being used in lead-acid
batteries and alkaline accumulators according to the state
of art as has been discussed above. It is, however, partic-
ularly advantageous to use the kind of lead dioxide electrodes
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being used in modern traction batteries characterized by
a very high porosity and with the active material arranged
in a matrix of a porous, resistant structure, for instance,
of porous polymer. It i8 also of advantage to use thin
positive plates which give high utilization of the active
material. In this case the cell will contain many electrodes
connected in parallel,
As an illustration of a battery having electrodes
in accordance with the embodiment shown in FIGURE 1, the
positive electrode can have the following composition:
prior to formation: 79 weight % PbO mixture, 16 weight %
K2SO4, 2 weight % polyethylene binder and 3 weight % graphite
(~ee further page 13, line 4-15).
The negative electrode can have the following
compoqition: 100 % sintered carbonyl iron powder (see further
page 12, line 8-9).
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The electrolyte can have the following composition:
l-N KOH saturated with K2SO4.
FIGURE 2 shows a design with bipolar electrodes.
The poqitive electrode material (13) is ~-PbO2 arranged on
the separating wall (14) and contained in a porous body
of nickel-plated iron. One may also dispose the active
material on the separating wall in other ways, for -instance
by means of pocket, grid, or tubular structures. These
structures may then be manufactured by nickel-plated
steel. This gives an important cost reduction for positive
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plates for power sources according to the invention com-
pared to the cost for positive plates for conventional
lead-acid batteries with an electrolyte containing sul-
phuric acid. With bipolar electrodes the electrode con-
ductivity is of less importance and the main function of
the structure is to keep the active material in position
and provide the electric contact with the separating wall.
The active negative material (15), in this case iron, is
manufactured according to the Swedish patent 360,952. The
cross-section of the cell if 420 cm2 and the cell pitch
2.6 cm, of which 0.5 cm refers to the negative material and
0,8 cm to the positive material. The electrolyte is in
charged condition 3-N with respect to KOH. Every cell
room contains 150 grams of K2SO4 in solid form at 25C,
discounting sulphate dissolved in the electrolyte. Bat-
teries according to FIGURE 2, where these main data give
energy densities within the range 2-300 KWh/m3 which ia
~everal times better than for conventional lead-acid batteries
and nickel cadmium batteries.
The positive electrode material may of course also
be generated by formation of, for instance, partially
reduced PbO, that is, lead oxide containing metallic lead.
This material is, according to the state of art, being
u~ed as a raw material in the manufacture of so-called
pasted, positive plates for conventional lead-acid accum-
ulators. A corresponding formation of positive plates for
alkaline lead accumulators according to the invention with
formation in alkaline electrolyte, however, with no special
additions of sulphate etc., to the formation electrolyte
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produces ~-PbO2 in the known way. During subsequent cycling
with electrolyte according to the invention may, however,
otherdifficultly soluble lead (IV) compounds be generated
in the charged electrode. A positive plate for the battery
according to FIGURE 2 can be made by formation of a PbO-
mixture in the following way. 2 kilogrammes of powdered
Pb, PbO of conventional battery grade, is mixed with 0.4
kilogrammes of finely ground K2SO4, then moistened with l-N
KOH and worked into the supporting electrode structure,
which could be known grid or mesh structures. The electrode
material i9 then let to mature for 24 hours at 80C in
wet air, after which formation is taking place in an
electrolyte consisting of, for instance, l-N KOH, l-N
KCH saturated with K2S04, or a neutral saturated K2S04
solution. Cycling i~ then taking place in l-N KOH saturated
with K2SO4, whereby the electrode in its charged condition
does not look entirely as a corresponding conventional positive
lead dioxide electrode, from which one may assume that the
active electrode material may contain other compounds than
~-PbO2. These compounds have, however, not been identified.
If the addition of K2SO4 to the electrode material is
replaced with an equal amount of K2S, there will be a more
pronounced difference in appearance. Electrodes with sulphide
additive give frequently higher capacity density than cor-
responding electrodes with sulphate additive. The lead (rv)
compounds present in charged electrodes with sulphide
additive have not been identified either.
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It should furthermore be added that it is suitable to
stabilize the structure of the electrodes described above in
the known way by means of polymeric binders, for instance,
with 2% polyethylene powder like Microthene MN 722~ which
is mixed into the electrode material prior to maturing, and
sintered at 120C. The electric conductivity may be improved
in the known way by addition of 3% graphite powder. The
recipes given above serve only the purpose to give a concrete
illustration of suitable positive electrodes for batteries
according to the invention.
Batteries in accordance with FIGURE 2 are conveniently
constructed with poles 8 and 9 on the sides of the casing 10,
these being connected to the terminal electrodes 33 and 34 of
respective polarity. Vent holes 11 and vented plugs 12 are
provided with the usual manner.
FIGURE 3 shows a portion only of an embodiment with bi-
polar electrodes of a large size for load levelling batteries.
In this case the batteries are built up of a series of pockets
(16) separated from each other by separators (17) and supporting
structures (18), and separating walls (19) for the bipolar
electrodes. The active materials (31) and (32) are added as
powders. The positive electrode material may then contain
addition of sulphate, sulphide, etc., as described above. It
is also suitable with these large electrodes to maintain a high
concentration of the anion in question during the whole discharge
step by means of circulating the electrolyte (51) through a bed (52)
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containing the salt in question. This bed (52) i9 pre-
ferably axranged in a qeparate vessel (53) as shown in
FIGURE 5 which illustrates such an arrangement with a bank
(54) of such batteries. The electrolyte (51) may then
preferably be introduced first into the negative electrode
material (31) in FIGURE 3 and thereafter into the positive
electrode material (32) via the separators (17). In this
way the alkalinity of the electrolyte entering the positive
electrode material will be somewhat reduced thanks to the
anode reaction during discharge which is of benefit for
the cathode reaction. This ~cheme is also of advantage
with the monopolar designs shown in FIGURE 1. Large cells
with monopolæ electrodes for e.g., load levelling, may in
practice be built as diaphragm cells used for the production
of chlorine and alkali, see e.g., the book "Chlorine",
ACS Monograph No. 154, by James S. Scone (1962) p. 94 seq.,
or U. S. Patents 2,987,463 and 3,591,483. The electrolyte,
e.g., l-N KOH, is saturated in separate vessel (53), the
saturator, with K2S04 at about 50C, and is then fed by
gravity into the anode space of the cell. The electrolyte
is fed by gravity from here via the diaphragm into the
cathode spaces, which contain the positive electrode material.
The electrolyte is then pumped back to the saturator and
again recirculated to the anode spaces of the cell. The
man skilled in the chlor-alkali technology will experience
no problems whatsoever applying his art in this particular
embodiment of the invention. It is, however, again empha-
si~ed that it has not yet been possible to identify which
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lead (rv) compounds are present in the positive electrode
under these conditions, which are characterized by an
elevated temperature and flow of electrolyte within and
through the electrode. This will reduce the concentration
gradients of the anion in question in the electrode, thus
creating a different environment compared to the case of
an electrode with a stagnant internal electrolyte phase.
The positive and negative active materials can have
the same compositions, respectively as in the embodiment
of FIGURE 2. These embodiments give high energy density,
low production cost and long life and are particularly
useful for load levelling.
FIGURES 1 and 2 ~how power sources in so-called
vented configuration, in which ca~e the charging gases being
developed particularly at the end of the charge leave freely
through the vent hold. It haQ also been found that power
source~ according to invention can preferably be designed in
sealed configuration. The negative electrode material, for
instance iron, can thereby be present in excess, in this
case counted on the first discharge step of the iron.
Qxygen developed during charge reacts with the active
electrode material. Hydrogen which may be generated
through self-discharge reacts unexpectedly ea-~ily with
the lead compounds in the positive material during the
conditions prevailing in the power source according to
the invention.
The invention can also with advantage be used with
smaller battery cells like sealed button cells and batteries
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with cylindrical shape. FIGURE 4 shows an enlarged cross-
section of such a button cell. The porous iron ancde
(20) and the porous lead dioxide electrode (21) are arranged
in two cans (22) and (23) which are isolated from each
other with an epoxy resin (24) which at the same time serves
as a sealing for the cell. The iron ele~trode has been
~intered directly in its can according to the description
in the Swedish patent 360,952. The active lead material
ha~ been put in as ~-PbO2. The separator (25) is a layer
of porous polyvinyl chloride. Cells of this kind can
be connected to batteries with any voltage and may be
u~ed in electronic apparatus like calculators, television
sets, etc. Cells of this type can also be made with a
fairly large diameter, for instance, 50 mm, and with vary-
ing electrode thicknesses up to 10 mm for the iron electrode
or above, and with corresponding thicknesses for the lead
electrode. Such so-called plate cells with square, rectangular,
or hexagonal form can be piled up to batteries for fairly
demanding application~ like power sources for electrically
power lawn mowers, etc.
Power sources according to the invention comprise a
new cla~s which i~ a bridge between the earlier known
alternative systems, that is the alkaline accumulators
and the lead-acid battery. Great possibilities exist
with knowledge of the spirit of this invention to design
and manufacture other power sources than those described
above for special applications using the state of art
within each field and the information given above.
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It iq recognized that the above description of power
source~ according to the invention give~ fairly large
advantages. One difficult problem with alkaline accumu- -
lators of nickel/iron type or the nickel/cadmium type is
the low performance of the nickel oxide electrode and
it~ high manufacturing cost. The fact that the alkaline
accumulators have but a small traction market is due to
these circumstanceq. Lead dioxide electrodes can be manu-
factured in a fairly simple way and in a large thickness
without decrease of the power density. On the other hand,
it i~ quite difficult to increase the thickness of the so-
called sintered nickel oxide electrodes. Therefore, so-
called pocket electrodes are preferred for systems with
high energy density which on the other hand have poorer
power den~ity and low energy density counted on volume and
weight, The new power ~ource with the po~itive electrode
of the ~ead battery arranged in an alkaline accumulator
therefore gives a very important increase of performance
and co~t reduction. The new power ource exhibit~ excellent
properties which count to more than a hypothetical average
for the lead-acid battery and the alkaline accumulator.
Although the invention has been described with
reference to certain specific embodiments it will be
apparent that these are illustrative only and that equivalents
and variations within the scope of the invention will sugge-~t
them~elves to those skilled in the art.
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