IMPROVEMENTS IN SECONDARY ELECTRIC BATTERIES OR ELECTRIC ACCUMULATORS
Year: 1885

page_text: I, CHARLES SCHANCK BRADLEY, of Yonkers in the County of Westchester and
State of New York, United States of America Electrician, do hereby declare the
nature of my invention for IMPROVEMENTS IN SECONDARY ELECTRIC BATTERIES
OR ELECTRIC ACCUMULATORS and in what manner the same is to be performed, to
be particularly described and ascertained in and by the following statement:-
The difficulty heretofore experienced in the use of Secondary Batteries has been
the great bulk and weight of such batteries compared with the amount of energy
which they are capable of containing; their deterioration and unreliability after
being used for a short time; their high cost; and the inconstancy of the current
produced by them due to the fall or decline in electromotive force, or to the increase
of internal resistance; and there has moreover been found to be a considerable loss
of energy, the electrical energy obtainable by discharging the battery being con-
siderably less than that required to charge it, and this loss increases with the time
which elapses between the charging and discharging.
The object of this invention is to overcome these and other objections, and to
produce a convenient, compact, and efficient battery capable of storing the maximum
amount of energy with the least possible weight.
The accompanying drawing illustrates the general arrangement and mode of
operation of the battery. Fig. 1, represents a vertical section of a single cell of the
battery in one of its simplest forms. Fig. 2, represents a vertical section of another
form of cell. Similar letters of reference refer to corresponding parts, in the two
figures.
In Fig. 1, D is a containing vessel or chamber of any convenient form or
material; in the bottom of this vessel is placed an electrode B, of carbon, platinum,
or other suitable material. A second electrode A, which may also be of carbon or
other suitable material, is suspended or supported in any convenient manner within
the vessel D, as shown. To the electrodes A and B conductors E and F are respec-
tively connected, these may be rods composed of the same material as the electrodes
to which they are attached. The cell is then filled to the proper level, as repre-
sented in the drawing, with the electrolyte which is a nearly saturated solution of
a metalic bromide. I have found that zinc bromide is particularly well adapted
to the purpose, and in the description which follows I shall assume that this salt is
employed as the electrolyte.

page_text: The battery is now in a condition to be charged, which is accomplished by con-
necting the electrode A to the negative pole, and the electrode B to the positive
pole of a dynamo-electric machine or other source of electrical energy, and an
electric current is caused to pass through the cell. The effect of this is that the
zinc bromide in the solution is decomposed by the electrolytic action of the current,
and the zinc is deposited upon the electrode A, and the bromine is set free at the
electrode B. The bromine thus set free is dissolved as fast as it is produced, it
being readily soluble in the solution of zinc bromide; and since the bromine is speci-
fically heavier than the zine bromide solution (density of bromine is about 3, the
average density of the zinc bromide solution is less than 2,) it remains in the lower
part of the cell near its own electrode and away from the electrode upon which the
zinc is deposited. When the decomposition of the zinc bromide has been carried to
the proper point, it is of course necessary to leave some of the salt undecomposed
in order to maintain a sufficient electrical conductivity, the battery is disconnected
from the dynamo, and it is now charged and ready to be used for any purpose
to which secondary batteries are applicable. When the battery is discharged the
action is exactly the reverse of what it is in charging. Zinc is taken up from the
electrode A, upon which it was deposited in charging and bromine is taken up from
the solution at the electrode B, and zinc bromide is thus formed, which goes into
solution. Finally all the zine and bromine which were set free in charging will
have recombined and the battery will then have to be recharged, and so on.
**
"3
In the arrangement described above, the bromine liberated in charging is kept in
place by gravity, as has already been explained, and since the density of the bromine
is about fifty per cent greater than that of the solution, which is a much greater
difference than that which maintains the separation in the common gravity
batteries, this arrangement will under ordinary circumstances be found to answer
very well. As a matter of fact no particular harm results even if the free bromine
comes in contact with the zinc, a piece of zinc may be kept for hours in a solution
of zine bromide in which free bromine is dissolved, without appreciable action.
But in case the battery is to be carried about or be subjected to shaking, or for
some other reason, it may be desirable to provide other means for separating or for
holding the fluids of the battery, for example, a porous cup or diaphragm may be
employed, in which case the form of cell shown in Fig. 2 may be adopted.
In Fig. 2, D is the containing vessel, in the bottom of which vessel is placed the
perforated electrode B, of carbon, platinum, or other suitable material, a porous cup
or diaphragm C is set into the vessel D and is supported by a ledge around the
inside of the vessel D, as shown. Within this porous cup another electrode A, of
carbon, platinum, zinc, lead, copper, or other suitable material, is suspended by
means of a rod of the same material, or in any other convenient manner. Con-
ductors E, and F, are connected to the electrodes A and B, respectively. The
vessel D may be provided with a cover G, as shown. The cell thus constructed is.
then filled with the electrolyte and charged and discharged in substantially the
same manner as already described in the case of the first form of cell. The porous
cup or diaphragm C, acts to keep the free broinine near its own electrode and
prevent its mixing all through the solution, but, as already stated this porous
diaphragm is not essential. The perforations in the electrode B, in Fig. 2, also
serve to confine the free bromine by forming cavities in which it accumulates.
Another advantage gained by having these perforations, is that the surface.
presented by the electrode is thereby increased.
In the foregoing description it has been stated that the bromine electrode of
the battery may be of carbon platinium, etc., and that the zinc électrode may
be of carbon, platinum, zinc, lead, copper, etc., and any of these materials can
be used and they answer the purpose very well. But there is a material
which is particularly well adapted to being employed for either or both of the
electrodes.
This material is described in the specification of my application for Letters
Patent No S076 of even date herewith and therefore is not claimed as forming any

page_text: part of my present invention although I proceed to describe it in order that it may
be fully understood in what manner I deem it advantageous to carry out my present
invention.
The material in question, as stated in said Specification N° 8076 AD 1885
consists of a mixture of gas retort carbon, or its equivalent, and gutta percha or
india rubber. The ingredients of the composition may be used in various propor-
tions, and various methods of mixing them may be employed, but excellent results
are obtained as follows: Two to ten parts of ground gas retort carbon and one part
of gutta percha or india rubber are thoroughly mixed and incorporated by rolling
in the well known manner in which gutta percha and rubber are usually worked.
The resulting material is then rolled, cut, pressed, inolded, or otherwise worked into
any desired form. It may be made plastic for this purpose by slightly heating it.
It is a well known fact that gutta percha and rubber may be vulcanized with
bromine as well as with sulphur, in fact a harder and less alterable material is thus
obtained. Consequently, if this material be used for the electrodes of the herein
described battery, the bromine set free in said battery, instead of destroying the
electrodes will actually harden and improve them. If desired the material may be
vulcanized before it is placed in the battery. A mixture apparently similar to the
above has been used before for packing and journals in machinery, which consists
of a mixture of graphite and india rubber, but this material is not a conductor of
electricity. This anomaly is due to the fact that graphite is soft and each particle
of it becomes coated with a film of rubber which is an electrical insulator and pre-
vents the particles from making contact, whereas gas retort carbon is hard and
sharp, and the points of the particles cut through the rubber and touch each other,
making electrical connection. A mixture of gas retort carbon and gutta percha
containing three or four parts of the former to one of the latter, is a good conductor of
electricity, baving a specific resistance only a few times greater than the gas carbon
itself, while a mixture of graphite and gutta percha having the same proportion of
ingredients, has a specific resistance several thousand times as great, which
increases the more the material is worked. The latter is practically a non-conductor
of electricity.
The herein. described battery it will be seen is extremely simple both in con-
struction and in operation, and this fact constitutes one of its most important
advantages.
A compound consisting of only two elements-a metal and bromine, is decom-
posed electrolytically, and the two elements are separated. The action does not
penetrate or eat into the electrodes and gradually disintegrate them as is the case
in most secondary batteries. The electrodes themselves are not affected when the
battery is charged or discharged, and there is no evolution of gases or formation of
insoluble matter, therefore when the battery is discharged it returns exactly to its
original condition, and the operation may be repeated indefinitely without in the
least deteriorating or altering the electrodes or the electrolyte. The chemical
affinity between zinc and bromine is very great, consequently the battery gives a
high electromotive force, and a small weight of material will store a large amount
of energy. The zinc bromide solution is a good conductor of electricity and the
internal resistance of the battery is therefore low, but if desired the internal
resistance of the battery may be made still less by adding a little hydrobromic
acid to the solution, in this way the resistance may be reduced to as low a point as
it is practically possible to obtain with any known solution, and this hydrobromic
acid also serves the purpose of replacing the small amount of bromine which may
be lost by volatization.
It has been found by actual trial that secondary batteries constructed and
operated in the manner above described give satisfactory results, but this invention.
is not limited to the particular construction or mode of operation set forth. For
example, it is obvious that containing vessels, electrodes &c., of various forms and
composed of various materials, may be employed, and any other suitable metallic
bromide besides zinc bromide may be used as the electrolyte, without departing

page_text: from the invention. It is also evident that instead of placing the electrodes hori
zontally, as shown, they may be placed vertically or at an angle; there may
moreover be various arrangements of cavities or porous diaphragms for holding or
confining the free bromine, and connection to the electrodes may be made in any
convenient way.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is
1. A secondary electric battery in which the electrolyte is a metallic bromide.
2. A secondary electric battery in which the electrolyte is zinc bromide.
3. A secondary electric battery in which the electrolyte is a solution of a metallic
bromide which is decomposed when the battery is charged, the metal being
deposited upon one electrode, and the bromine being set free at the other
electrode.
4. A secondary electric battery in which the electrolyte is a solution of zinc
bromide, which is decomposed when the battery is charged, the zinc being deposited
upon one electrode and the bromine being set free at the other electrode.
5. A secondary electric battery in which the electrolyte is a solution of a metallic
bromide which is decomposed when the battery is charged, the metal being deposited
upon one electrode and the bromine being set free at the other electrode, the
bromine thus liberated being taken up by the solution.
6. A secondary electric battery in which the electrolyte is a solution of a metallic
bromide which is decomposed when the battery is charged, the metal being deposited
upon one electrode, and the bromine being set free at the other electrode, the two
electrodes being separated by a porous cell or diaphragm which prevents the
bromine from coming in contact with the metal.
7. A secondary electric battery in which the electrolyte is a solution of a metallic
bromide which is decomposed when the battery is charged, the metal being deposited
upon one electrode and the bromine being set free at the other electrode, the
electrode upon which the metal is deposited being placed above the one on which
the bromine is set free, whereby the free bromine tends to remain near its own
electrode and to be kept away from the electrode upon which the metal is
deposited.
8. A secondary electric battery wherein one or both electrodes is or are formed
of the herein described electrical conducting material consisting of gas retort carbon
or other carbon which is hard and sharp and gutta percha or india rubher.
9. A secondary electric battery wherein one or both electrodes is or are formed
of the herein described electrical conducting material consisting of gas retort carbon
or other carbon which is hard and sharp, and gutta percha or india rubber, said
gutta percha or india rubber being vulcanized with bromine.
Dated this 94th der of Tobruary 1885