Process for the Production of Electrode-plates for Secondary Batteries.
Year: 1895

page_text: Date of Application, 12th Mar., 1895-Accepted, 12th Mar., 1896
Process for the Production of Electrode-plates for Secondary
Batteries.
I, CARL LUCKOw, Chemist of Deutz near Cologne in the Province of Rhine-
laud and Kingdom of Prussia 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 :-
My process is as follows:
I make cells of bright plates of as pure soft lead as possible, in vessels or boxes
in such a manner, that the plates stand or are hung up alternately as positive
(anodes) and negative electrodes (cathodes) insulated and at intervals of
about 10 to 15 m/m opposite to each other. I fill up the cells thus made with the
strongly diluted solutions of the salts which are more particularly described later
on, as electrolytes: Through these cells, of which I can according to the nature
and strength of the source of the current, insert a corresponding number, one
after the other, or parallel to each other, I cause an electric current of only
moderate strength-corresponding to the surfaces of the plates-to pass without
interruption, at first in one direction. The positive, i.e. the plates connected with
the pole of the source of the current now become covered at the cost of their
bright lead interior with a layer of peroxide, while the negative plates remain
bright.
Immediately on the current being put in circuit there is formed uniformly on
the surface of the positive electrodes clearly perceptible an at the beginning
delicate layer of brown peroxide of lead, which with the continuance of the
electric current through the cells becomes visibly darker and thicker; and after a
few hours the new fairly thick layer of peroxide assumes a deep black brown
colour.
After about 5 days, the layer of peroxide, on the strength of the current being
reduced, has attained a sufficient thickness on the + plates, for the latter now to be
used as pole-plates in secondary cells; in this remarkably short time the originally
bright electrodes are softened so deeply and very uniformly by the extremely
energetic oxidation, so to say in layers from the outside towards the inside, that
they are made eminently capable of being used as electrodes in secondary cells for
the reception of the current in a very high degree. When this point has been
reached, the plates thus formed are taken out of the salt baths, lixiviated in slowly
Howing water and may now be used as electrodes in secondary cells. The secondary
cells are filled with a diluted sulphuric acid of from 1-15 to 1·17 sp. gr. and the
processes in the same on being charged and discharged are well known.
The formation of the electrodes, that takes place before the building up of
the secondary cells therefore consists in the rational production of a sufficiently
strong and adhesive layer of peroxide on the bright lead plates under the
influence of the electric current in special formation-cells; it is only a process of
formation that I wish to be protected by patent rights, strength and tension of the
current.
The strength of the current is essentially regulated by the energy, with which
the different strongly-diluted solutions of salt-in the foremost place the acids and
salifiable bases of the salts or mixtures of salt-are able to oxidize the anodes and
care must be bad that the generation of oxigen is not too great at the anodes i.e. that
too much electric energy is not lost in the oxidation. The oxidation which is hastened
by strong currents is not in any way in proportion to the increased consumption of

page_text: current and has besides the great disadvantage, that the layers of peroxide
produced become brittle and do not in consequence of the excessive generation of
gas adhere sufficiently to the solid core of the anodes. A very intimate connection
(contact) of the active layer with the bright metal of the anodes is a sine qua non
for the storage of the current. According to the salts or mixtures of salts of the
strongly diluted electrolytes, I therefore use weak currents of at the most one
ampère for 2 to 3 square cm. of one-sided anode surface.
The tension in the cells, when the current passes through depends on the
efficiency of the electrolytes i.e. on the interior resistance in the cells. The latter
depends on the degree of dilution, the salts or mixtures of salts of the electrolytes
and by the space between the pairs of electrodes. With a degree of dilution of
the salt baths of only 15% of anhydrous salts and with an interval of 12m
between the pairs of electrodes, the tension in the cells, on the current passing
through, is according to the kinds of salts and the reaction of the electrolytes,
roughly speaking, from about 2 to 3 volts. A dynamo-engine of a tension of
180 volts is therefore able to decompose from 50 to 60 of such cells, when placed
one behind the other.
As electrolytes I use strongly diluted weak acid or neutral or weak alkali
solutions with a fixed percentage of salt viz. :
1.) Of the salts of all the light metals and of ammonium during the decom-
position of which by the electric current no products of decomposition appear at the
positive pole, which have a disturbing or retarding influence on the formation of
peroxide.
2.) Of the double salts or salt mixtures of the light metals with each other and
with the ammonium with the afore-mentioned properties.
3.) Of the salts of the heavy metals, their double salts or salt mixed with each.
other or with the light metals and the ammonium it being taken for granted, that
it has the above mentioned qualities and in which the separation of metal at the
negative pole either does not take place at all or can be prevented by a small
addition of free acid.
By light metals those metals are understood whose oxides are heavier and by
heavy metals those whose oxides are lighter than the elements.
The compounds especially used are the soluble simple salts and the soluble
double salts of sulphuric acid or phosphoric acid or hydrochloric acid combined with
potassium, sodium, strontium, calcium, barium, magnesium, aluminium, manganese,
chromium, iron, nickel, cobalt, uranium, zinc, or cadmium.
Besides these salts, the solutions may contain a certain quantity of such acids
which produce no precipitate when brought to the solution of the salt. For
instance, if a solution of the mentioned salts of potassium or sodium is used,
sulphuric or hydrochloric or nitric acid may be added to the solution; if a solution
of the mentioned salts of strontium calcium, barium is used, hydrochloric or nitric
acid may be added, but not sulphuric acid, because sulphuric acid combines with
the said three metals producing insoluble sulphates.
Iustead of free acids, caustic alkali, i.e. caustic potash, or caustic soda, or caustic
ammonia, also may be added to the solution, if by this addition, no precipitate
is produced; for instance if the mentioned salts of potassium and sodium are used.
The advantages of my process in comparison to those hitherto in use will now be
explained.
The formation of bright lead plates, with the object of using them later on as
pole plates, in secondary cells in diluted sulphnric acid according to the directions
of Planté, is excessively dear and not very rational on account of the long time
needed. The diluted sulphuric acid only breaks up very slowly under current, a
continual circuit of the current being at the same time necessary, the solid lead of
the anodes by the formation of a layer of peroxide only up to a certain degree and
with a hardly perceptible increase; this active layer is however always made very
impure by inactive crystalline sulphate of lead, which the peroxide shows by its
lighter colour.
It is however just the bad-conducting sulphate of lead that so

page_text: greatly retards the oxidation of the lead at the anodes and finally puts a stop to
any further increase of the active layer, as the sulphuric acid is now able to oxidize
large quantities of sulphate of lead at the anodes.
Thus the formation of bright lead plates in diluted sulphuric acid of a specific
gravity of from 1.10 to 1.17, at which density the formation takes place the
quickest, takes roughly speaking 9 months in order to render the plates capable of
so great a reception of current, that they can be applied as electrodes in secondary
cells. At the same time a continual circuit of the current is imperatively necessary,
because the sulphuric acid is much more easily able to reduce than to oxidize
the sulphate of lead, which together with the peroxide is continually forming on
the anodes.
I, on the contrary, with my process form such plates in about 5 days with only a
moderate current, by which means an enormous saving in time and work and cost
of production is effected.
The effective layers of peroxide produced on the anodes by the electrolysis of my
strongly diluted or only weak acid or neutral or only weak alkali solutions of salt
never contain any traces of sulphate of lead, for they are perfectly pure and are
not crystalline they adhere in intimate connection firmly to the heart of the
electrodes and are nevertheless in a state of distribution than which a finer one
cannot be imagined. Here in the most ideal manner are joined together all the
qualities so necessary for the storage of the current in order to give the electrodes
a hitherto unattained capacity for receiving the current. The incomparable purity
of the peroxide produced by my process is made specially perceptible by its deep
brown black colour.
Even Planté essentially reduced the time occupied by his process of formation
by an accurately fixed addition of nitric acid or acetic acid to the diluted sulphuric
acid; these two acids however have a rather high price and decompose themselves
continually in the course of the formation, so that a continual addition of the nitric
as well as of the acetic acid becomes necessary whereby the advantage of the
shortened formation is almost counter-balanced. The sulphuric acid is easily
reduced under the influence of the current at the pole to nitrous acid and even
to ammonia, while the acetic acid decomposes itself at the + pole to carbonic acid.
After the formation the nitric or acetic acid must be entirely removed again by a
troublesome process from the formed plates in order to prevent any injurious
influences, when these plates are used later on as poles in the secondary cells.
Planté says himself, that the active layer produced in this accelerated way of
formation did not adhere firmly enough to the electrode. Even if the fixed
additions of those two acids to the diluted sulphuric acid are strictly adhered to,
still it is not possible to produce a pure peroxide of lead, for the latter becomes
more or less impure even by sulphate of lead. Next to the greatly accelerated
formation the chief advantage of my process lies in the fact, that by far the greater
number of the strongly diluted solutions of salt used by me, as for instance the
neutral or weak acid ones or neutral or weak acid sulphates, phosphates, borates,
the weak alkaline chlorides do not decompose during the formation but continually
regenerate themselves in the process of the electrolysis and may therefore always
be applied again for purposes of formation, and can hardly be used up. The
necessary filling up of this strongly diluted electrolyte, which is done, and the
lixiviating of the formed plates is hardly worth mentioning. Then I may mention
in favour of my process the extraordinary cheapness of most of the salts used in it
as for instance, glauber salt, Epsom salt, rock salt, especially as the solutions of
these salts are only used in a very diluted form.
Some further essential advantages of my process are that the active layers of
peroxide adhere firmly to the bright plates, do not separate, while in work in the
cells from the electrodes thereby causing the latter to last a long time, and above
all things possess a great current-absorbing capacity, which according to determina-
tions from experiments made on a large scale amounts to at least from 3 to 5 times
that which could at all be obtained by the processes hitherto in use.

page_text: The nature and the peculiarities of my invention consist of as follows:
The extraordinarily characteristic and energetic action in the formation of the
layer of peroxide which is active in storing up the current is only obtainable with
the above-mentioned solutions of salt; firstly when the salt baths are only slightly
acid or neutral or slightly alkaline and then at the same time-this circumstance is
the most essential and important of the invention--are in a state of accurately
fixed solution.
The more acid the electrolytes are beyond a certain limit, i.e. the more free acid
they contain, the slower, more incomplete and less uniformly the formation of the
layer of peroxide takes place, the more impure and crystalline the latter, becomes
and the lighter, in consequence its colour.
The more alkaline the solutions of salt are made beyond a certain limit, the
more scanty, spongy, watery and lighter in colour the peroxide becomes which the
current produces on the anodes; in solutions of salt which contain free bases in
excess, the oxidation of the lead on the anodes gradually disappears entirely ;
the latter gradually are dissolved and the current acts upon the lead on the
cathodes.
But only with a characteristically accurately limited degree of dilution of these
slightly acid or neutral or slightly alkaline electrolytes does the current attain the
height of its oxidizing force, and the acceleration of the formation is increased to
the highest possible attainable degree. This most suitable fixed percentages of
salt amount according to the kinds of salt to from 1% to 3% of the anhydrous
salts; and the quantity of the free acids or caustic alkali must not exceed one and
a half per cent. of the solution. The use of such strongly diluted electrolytes forms
solely the characteristic feature of the invention.
If one gradually dilutes these solutions below these percentages, the action of the
current of the formation of the layer of peroxide becomes by degrees weaker with
the higher inner resistance of the cells. Much more peculiar however and more
characteristic is the phenomenon, surprising in a high degree, which takes place if
these electrolytes are gradually concentrated beyond the above-mentioned percent-
ages of salt, since with the slightest increase of strength, the oxidation at the
anodes diminishes with a sudden and truly startling decrease.
If for instance comparative experiments are made with solutions of Epsom salt
and glauber salt, the latter salt being in neutral or slightly acid solution, it will be
found, that the current produces entirely pure peroxide of lead on the anodes only
with a percentage of salt of the electrolytes lying within the above-named limits,
while with a gradual dilution and more especially with an increased density of the
electrolytes the rapidly diminishing layer of peroxide is rendered more and more
in pure by sulphate of lead. The latter already begins to appear with a slight
percentage of salt such as 0.5% in white spots and stripes on the anodes, so
that the latter with a salt percentage of the electrolytes of less than 0.2% are
entirely covered with sulphate of lead and shows no further trace of peroxide.
In the same manner there is always more sulphate of lead contained in the layer
of peroxide, which is produced more and more scantily and less uniformly on the
anodes when saturated solutions of these salts are used in the electrolysis. If
similar experiments are made with very weak alkaline solutions of rock salt, then
chemically pure peroxide of lead is only obtained with fixed low salt percentages
of the bath, while on the dilution or the density being increased greater and greater
quantities of white chloride of lead appear at the + pole with the continually
decreasing oxidation.
This very peculiar fact is explained that in a state of weak dilution of these
solutions of salts the component parts of the salts, according to the kinds of salt
are only loosely joined together. Strong acids or salifiable bases combine with
strong salt bases much more closely than weak acids or salifiable bases with weak
bases; the former salts therefore need to be more diluted than the latter in order
to attain a certain degree of dissociation.
In a very greatly diluted solution of borax, for instance, the water displaces the

page_text: boracic acid entirely and the solution is like a diluted solution of sodium hydroxide
in which boracic acid hydrate is in solution, without being combined with sodium.
The electric current therefore does not need to perform any decomposing action,
when flowing through such salt baths, as it does when passing through concentrated
electrolytes, but may at once concentrate its whole energy on the oxidation of the
anodes, whereby naturally the formation of peroxide of lead is accelerated in the
highest degree.
The intense oxidation at the + pole is furthermore greatly assisted by the
tensions at the poles, a simultaneously occurring decomposition of water and
therefore the formation of oxygen in the neutral and slightly acid as well as of
peroxide of hydrogen in the weak alkaline solutions. In the greatly diluted
electrolytes the bright lead anodes also are covered with a film of peroxide as soon
as the current is put in circuit, while the peroxide only appears after the current
has been acting for a long time, in more saturated electrolytes.
If the formation is continued for a long time, the inner heart of lead of the
positive pole-plates also does not remain without being acted upon by the
energetically oxidizing action of the current in these greatly diluted solutions of
salt, and the plates are converted into absolutely pure and deep black-brown
peroxide. But in order to be able to use the formed plates as pole-plates_in
secondary cells the formation must of course be interrupted in time, and in order
to increase the length of time that the electrodes last, a sufficient thickness of bright
metal for the heart of the plates must be allowed; the pure metal heart being
intended to serve as a good conductor of the current and the durable bearer of the
active layer.
A plate of lead, that is formed too far, for instance of pure peroxide of lead
would soon fall to pieces while at work in the secondary cells.
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:
Process for the production of electrode-plates for secondary batteries according
to which bright plates of lead are subjected to a preparatory treatment in vessels
specially set apart for this purpose before the building up of the secondary cells,
the treatment being distinguished by the application of strongly diluted, slightly
acid, neutral or weak alkaline solutions of fixed percentages of salt of the following
salts as electrolyte.
As salts are used:
a) The salts of all the light metals (i.e. of those metals, whose oxides are
beavier than the elements themselves) and of ammonium, during the decom-
position of which by the electric current no products of decomposition appear
at the pole, which have a disturbing or retarding effect on the oxidation
of the metallic lead.
b) The double-salts or salt-mixtures of the light metals and of ammonium
with each other and having the above named qualities.
c) The salts of the heavy metals (i.e. those metals, the oxides of which are
lighter than the elements themselves), their double-salts or salt mixtures
with each other, or with the light metals and the ammonium the above
named qualities being taken for granted and in which a separation of metal
at the pole either does not take place at all or may be prevented by a
slight quantity of free acid.
Dated this 9th day of March 1895.
For CARL LUCKOW,
Bernh. Brockhues.