A New or Improved Method of Manufacturing Electrodes for Secondary Electric Batteries.
Year: 1896

page_text: Date of Application, 11th Jan., 1896-Accepted, 14th Mar., 1896
COMPLETE SPECIFICATION.
A New or Improved Method of Manufacturing Electrodes for
Secondary Electric Batteries.
I HENRY LEITNER, of 11, Lindenstrasse, of Niederschönhausen near Berlin
in the Kingdom of Prussia German Empire, Philologer, do hereby declare the
nature of this invention, and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement :-
This invention relates in general to a secondary electric battery or cell, which in
comparison to its capacity possesses a very low weight, and which after having
been electrically charged may remain unused for a very long time without under-
going any material change in the chemical or mechanical constitution of its
electrodes; there are during this time of rest no chemical re-actions whatever, and
there is also during the time of discharge no appreciable development of vapours
or gases. These advantages are arrived at by using electrodes, especially positive
electrodes, of a special, kind or nature, and my invention relates, therefore, in
particular to the method of manufacturing these said electrodes.
My method consists, briefly, in first, finely powdering and intimately mixing a
combination of lead, preferably oxide of lead with carbon; second, converting
that mixture into a pulp or stiff paste by aid of a suitable medium, such as
molasses, linseed oil, but preferably glycerine, which gives a chemical reaction with
the lead oxide; third, forming said pulp into flat or curved plates; and, fourth,
reducing the latter electro-chemically to porous lead. Said four phases are
followed by a fifth, which consists in subjecting said porous plates to pressure;
these processes are more fully described hereinafter.
In order to make my invention more clear, I refer to the accompanying drawing,
in which similar letters refer to similar parts throughout the different views, and
in which :-
Figure 1 is a view of a thin flat pierced plate of lead covered with a thick layer
of the said pulp (phase 3);
Figure 2 is a similar view showing a modification, the plate of lead-foil being
replaced by lead meshes on both sides;
Figure 2 shows a portion of an electrode having the lead net work placed in the
centre of the mass;
Figure 3 is an upper view of a curved electrode;
Figure 4 shows the same electrode placed in a receptacle.
Figures 5 & 6 are similar views representing the positive electrode in two
different stages, and
Figure 7 is a vertical section through a secondary element manufactured according
to my invention.
In carrying my invention into effect, I first produce a very intimate mixture of
95 portions of oxide of lead with 5 portions of retort-carbon by grinding both
materials simultaneously in a suitable apparatus, preferably in a mill, and I then
add to said mixture 25 portions of glycerine; this mass is then kneaded until it
becomes stiff. When commencing to become stiff, a spontaneous heating of the
mass indicates, that a chemical reaction between said glycerine and the oxide of
lead takes place; after said reaction is completed, the mass is no longer mouldable
or plastic, but is hard and brittle.
Before letting the mass assume this state, it is distributed in a somewhat thick
layer (a, Fig. 1) upon a thin sheet of pierced lead (b, Fig. 1) or preferably upon

page_text: both sides of a piece of lead net-work (63, Fig. 24) with wide meshes; after which
it is allowed to become hard and dry. The plate thus formed is now subjected for
about 100 hours to the action of an electric current in a bath containing sulphuric
acid, and the compound of oxide of lead and glycerine is thereby reduced to lead,
this lead being, however, perfectly porous (but not spongy), and having a fracture
very similar to that of carbon. During these electro-chemical reactions, acrolein
and acrylic acid are freely produced, so that the electrolyte should be changed
from time to time, and after the completion of the process. Every trace of free
glycerine, acrylic acid, aldehyde etc. must be carefully washed out or otherwise
removed.
Although the plate when in this state might be used as an electrode, it is
preferable to subject the porous lead-plate to a strong pressure in moulds so as to
increase the density of the same. In this state the porous lead is so extremely
plastic that it may be pressed into any shape, for instance into the cylindrical
shape (a b, Fig. 3). I prefer cylindrical electrodes as I then attain the special
advantage, that the internal expansion forces coming into play within the electrode,
and tending (in a plate) to deform the same, are caused to act in a useful and
desired direction. This peculiar behaviour will appear more clear, if it is borne
in mind, that on transforming lead into superoxide of lead, the bulk of said lead is
increased, and that, further, the degree of increase is the greater, the greater the
mass of lead contained within a given volume. If, therefore, the pores of the
porous plate of lead are diminished in size-not in number-the volume of the lead
becomes correspondingly smaller, but the quantity of lead to be converted into
superoxide of lead is just the same as before. When, thereafter, said compressed
porous lead is turned into superoxide of lead, the volume or bulk of the latter
becomes considerably larger, but not so large as if the porous plate had not been
compressed.
There results from said limited increase in bulk a very strong coherence of the
particles of superoxide formed, and an electrode is thereby secured capable in a
high degree of resisting destructive influences.
There results further (provided the electrode as well as the vessel (c Figs. 4-6)
containing the same be circular or cylindrical) an increase in the curvature of said
electrode, or an elongation of the radius of curvature respectively, in consequence
of which said electrode presses itself firmly and tightly against the wall of the
vessel (Fig. 5). The proper shape of the electrode cannot from that moment alter
any more, provided, there be left between the vertical edges of the electrode (a2 b)
a slot allowing of a sufficient radial expansion of the said electrode (Fig. 6).
I wish to call special attention to the fact, that the uniform curving and
lengthening of the finished electrode (on having its lead converted electrically into
superoxide of lead) depends greatly on the fineness of the pulverisation of the
oxide of lead and retort-carbon originally employed, and on the uniform distribution
of said retort-carbon within, or among, said oxide of lead. Great care should,
therefore, be taken with regard to the latter two points; the same attention
should, of course, be paid if the electrodes to be produced are flat. The uniform
reduction of said mixture to porous lead, and the uniform distribution of the pores
within the resultant lead entirely depend on the care exercised in these respects.
A peculiar feature of my novel positive electrodes consists in the fact, that the
reduction does not commence at the side or surface having the thin plate of lead b,
or the pieces of net ¹ respectively, attached to it, but at that side or surface,
which is farthest away. If the electrode is made with a net work of lead in the
middle of the mass (63, Fig. 2A) said reduction commences also at the two outer
surfaces.
The oxidation of the reduced plate on charging the accumulator proceeds
similarly from the outside to the inside. The innumerable fine particles of carbon
cause the current to perform its work with perfect uniformity about the whole
outer surface of the (straight or curved) electrode, and from thence perfectly
uniformly through the whole mass.

page_text: If cylindrical electrodes are to be produced, I prefer to bend the electrode under
pressure in moulds after the mass (consisting of oxide of lead, retort-carbon, and
glycerine) has been reduced to porous lead. The plate after being treated in the
nanner just stated is at first flexible or pliable, but becomes after some hours hard
and brittle, so that no bending whatever of the plate can then take place. The
fact, that the electrode after being pressed and bent becomes spontaneously hot,
shows, that again a chemical reaction occurs within the same. This may well be
explained by parts of the electrolyte (sulphuric acid) remaining within the mass,
or being sucked up by the particles of carbon, becoming now concentrated and in
the presence of oxygen of the air giving rise to local electro-chemical reactions
between the lead and carbon ingredients of the plate. After the hot electrode
has cooled, it is, as mentioned, hard and firm (though brittle) and of less weight
than before; at the same time it retains its perfect electrical conductivity.
Having now finished the description of the positive electrode, I proceed to
describe, for the sake of completeness, the negative one. The latter is composed
of a rod d (Fig. 7) consisting preferably of ebonite. This rod is covered to within
a few inches of the bottom with a piece of tube consisting of lead. This piece
of tube is first amalgamated, and then a layer g of zinc is electrolytically deposited
thereon. The amalgamation as well as the electrolytic covering with zinc should
be repeated several times. By first covering the negative electrode that way,
I attain the advantage, that the zinc deposited thereafter in charging is more
evenly deposited, and that then it is only this latter zinc which is consumed on
discharging the cell. The negative electrode is suspended by means of the cross-
stay e, that is itself supported by the receptacle c.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
1. The method of manufacturing electrodes for secondary electric batteries,
consisting in finely powdering and intimately mixing oxide of lead with carbon,
turning that mixture into a pulp by aid of a suitable medium, forming said pulp
into flat or curved plates, and reducing the latter to porous lead by exposing them
to the action of an electric current, for the purpose as described.
2. The method of manufacturing electrodes for secondary electric batteries,
consisting in finely powdering and intimately mixing oxide of lead with carbon,
turning that mixture into a pulp by aid of a suitable medium, forming said pulp
into flat or curved plates, reducing the latter to porous lead by exposing them to
the action of an electric current, and subjecting said porous plates to high pressure
in moulds, for the purpose as described. "
3. The method of manufacturing electrodes for secondary electric batteries,
consisting in finely powdering and intimately mixing oxide of lead with retort-
carbon, turning that mixture into a pulp by glycerine, forming said pulp into
plates, reducing the latter to porous lead by exposing them to the action of an
electric current, subjecting said porous plates to pressure, and bending them into
cylindrical shape, for the purpose as described.
Dated this 11+
Ton 1906
HENRY LEITNER,
By Geo. Thos. Hyde,
1, Broad Street Buildings, Liverpool Street, London, E.C.,
Agent for the Applicant.